In the world of guitar and bass, we've seen, thought about, and woke up screaming to the thought of some crazy modifications to guitars and basses. This is where the tech minded get abstract. Without getting too balls-deep into modding out tone caps and pot values, we'll take a look at some of the more awkward mods we've seen, practiced, theorized, or read about.
Gibson With Filter'Trons: We have had experience with Les Pauls and SGs, and we've had experience with Filter'Trons. In general, Filter'Trons are renown for giving Gretsch guitars that shimmer; not as barky as a Strat, or as bright as a Ric, but a sound all it's own. People have asked the question "If I put Filter'Trons in my Gibson, can I get a Gretsch sound?" No. What one must keep in mind with Gretsch is the other key to their sound is the hollowness of their bodies (even if chambered), and the wood. Gretsch is a company that uses a lot of maple, not so much mahogany. They are inherently a brighter guitar. That said, people have experimented with this. Essentially, you'll get a clear, bright sound out of the Les Paul, one that's great for cleans, and more transparent with drive. To me, they sound a bit like what my brain tells me a '57 should sound like, but brighter and clearer. The bridge pickup isn't as harsh as a Gibson 498. With an SG, it'll be in the same ballpark as the LP, but less snap, due to the all-mahogany body.
To achieve adding Filter'Trons with minimal hacking of the Gibson (or Epiphone), we recommend going with TV Jones pickups, and Classics will be the most traditional with standard output. These are more expensive than Gretsch HS Filter'Trons (which we love), but have the "English mount" option to install them without drilling, and are considered a step up from HS. GFS has their Nashville, which is Filter'Tron-esque, but has ceramic magnets, so doesn't quite match the full Filter'Tron sound (Filter'Trons have alnico), but is a budget-orientated way to get the sound.
Another mod to consider in this arena is Seymour Duncan SH-3 Stag Mag pickups. Set these up with coil splitting, and you're working Strat pickups on a Les Paul without HEAVY modification of the body. GFS does have some Humbucker Rout Adapter Rings for putting actual Strat or Tele pickups in a Gibson with pickup bezels.
P-90's and Mini-Humbuckers: P-90's are being found in all kinds of guitars these days. We've come across some parts-casters (home-built Fender style guitars made with various Fender and/or aftermarket parts) that have had them, as well as (duh) the Gibson lineup. The Les Paul Juniors with the all mahogany seem to be the best home for these over-sized single-coil pickups. If you like bright noisy and aggressive, this is a great way to achieve it. That said, the flip side of these is that the sizing of P-90's is so unique that you're limited to mods on P-90 equipped guitars. There are some P-90 sized humbuckers if you want to switch sounds, and what you'll find is a satisfying humbucker sound that correlates with that guitar.
Conversely, most of the pickup makers are making humbucker-sized P-90's. The ones we see the most are Gibson P-94, and the more reasonably priced Seymour Duncan SPH90-1 Phat Cats. GFS also has some for the budget minded. There's some debate as to how close these are to actual P-90's, but they will get you into the P-90 zone without butchering a guitar. Duncan also has their SHPR-1 P-Rails, which is like a P-90 with an extra rail to give you some hum canceling. This can be split to just have the faux P-90 going, and stay in the realm of the true sound.
There are some stacked P-90's as well, which look just like a P-90, but have a second coil under the top to achieve hum-canceling, similar to how a Fender Noiseless pickup works. There's Seymour Duncan's STK-P1, and Gibson P-100 and H-90. Though we don't know much about the Duncan, we do know the Gibson ones blow. Hard. Very muddy pickups, and not P-90 sounding; more like a bad humbucker. Also, if you install these on a P-90 guitar, the standard rout may not be deep enough for these. If the guitar has a stacked P-90 style pickup and you want to put real P-90's in it, the route may be too low, suspending the P-90 too high above the bottom of the guitar.
With guitars equipped with P-90's, there is the mini-humbucker option. That said, there are fewer offerings for mini than standard humbucker options. Duncan has some in their Antiquity line, and GFS has some as well. Mini-humbuckers go back to the time when Gibson bought Epiphone. There was a stockpile of Epiphone bodies, but Gibson didn't have humbuckers that would fit in them. As a result, Gibson designed the mini-humbucker. Every so often, Gibson will release a model of LP with mini-humbuckers, but they aren't extremely common. That said, we would never condone routing a humbucker guitar for mini-humbuckers. Not that we don't like minis, but mainly because you already have several options in standard humbuckers as it is. At the same time, we'd never route a P-90 guitar to put humbuckers in it. These look horrible, and destroy the resale of the guitar.
Another thing to keep in mind is that there are several builders that use P-90's, not just Gibson. Music Man has an Axis Sport model with them, and some of the Eastwood models have sported P-90's. If you look around, you can find some interesting offerings.
The Strats we've come across that have had P-90's have had an interesting sound, yet still have that Strat quality to it. Basically, the P-90 on a Strat will sound fairly bright, but not have that Strat "quack" as much.
Rickenbacker Mods: We have seen some mods done to Rics, and they generally ruin a great guitar or bass. We don't see a lot of aftermarket Ric guitar pickups, and Seymour Duncan and Alembic are the only companies we've seen that do an aftermarket for the basses; the Duncan SRB-1, which is designed to be a hum-canceling Ric pickup, and the Alembic turns a Ric into an active bass. Generally, anyone buying a RIC is buying the sound... and quirks. These aren't guitars for modding. They have their own sizes of pickups, and changing them out with something else requires heavy modification.
Conversely, GFS has their Memphis and Liverpool model humbucker sized pickups that are supposed to get some Ric sound.
Gretsch: We have had some fun in the past upgrading the Gretsch 5120's. These were the low-end Gretsch hollowbody guitars that were built extremely well, but came with horrible stock pickups that we call "Gretschbuckers". The mods done to 5120's were generally done to make it more like a pro-line Gretsch. The end result was a guitar that sounded like a 6120, and was only missing the bracing, the F-hole binding (though many found ways to do some great faux binding), and had a black headstock (some figured out ways to fix that too). The 5120 has been discontinued, and the replacement 5420 has Blackout Filter'Trons on them. That said, there are still plenty of people who will replace HS Filter'Trons with TV Jones versions. The true Gretsch zealots will argue up and down that the TV Jones pickups are WAY better than the HS Filter'Trons, and there is a bit more clarity to the TV Classics. We like the sound of good ol' HS Filter'Trons enough that it's not worth our time to replace them. TV Jones does quite a few offerings in Filter'Tron style pickups with increased output and such.
Other Gretsch guitars have come stock with P-90's and Duosonic pickups, which still have some Gretsch characteristics, but aren't as warm.
Fender: The great thing about Fender is that most of the weird mods you can think of with them, they've released a model that had it at some time or another. There's a Tele with TV Classics on the market, there are some Strats with different switching and active tone, and the Humbucker equipped Strat is quite common. Generally, if you start modding Fenders too much, you're gonna get a superstrat sound; think Jackson, Charvel, old Kramer, or Ibanez. The Seymour Duncan SH-4 JB is a sound we're very familiar with in a Strat.
Some interesting mods we've come across are some phase-shifting, adding of kill-switches, and other toggles added to a pickgaurd. There have been effects added to Strats and one P-bass we've come across, though we wouldn't recommend this. One mod that's a little outside of the box involves replacing the 5-way switch with a 7-way, which adds the ability to run just the neck and bridge pickup (without the mid), and all 3 pickups.
The beauty of Strats is the pickguard. You can take off the original, and get an aftermarket one in the color you want, and hack and slash the hell out of it to put whatever you want on the guitar without touching the wood. We also like blocking the trems on Strats, as we, and 90% of our peers never use them anyway. when doing a partscaster, we look to finding "hardtail" bodies, bodies that take a standard bridge rather than a trem. These usually tend to be string-through-body like a Tele.
With Teles, we don't care to mod these in that the beauty is the simplicity of the guitar. We've seen some with trems added; mainly Bigsby variations, which change the overall sound of the guitar. One shop owner put it best when he said "A Bigsby makes a Tele sound even more like a banjo". There's also the B-Bender, which is a machine that puts a spring-loaded armature in the guitar at the top strapbutton, inside the body. The idea is that you pull down on the guitar, and the B-Bender bends just the B string. This can be heard in Led Zepplin's "All of My Love". The worst part of this mod is how much body you route away for a stupid effect. Translation: we wouldn't do it. Ever.
We have seen some people swap Tele necks for Strat necks, or P-bass necks for Jazz necks. A neat little mod that makes the guitars stand out, and makes the guitar or bass more playable to the player. The nice thing is most Fender neck pockets are standard, and this can be done without alterations to the joint area.
Superstrats and Pointy Guitars: Generally, we don't mess around with (or use) these too much. Basically, we say don't put holes in the body of these unless you don't care for the resale value. Otherwise, you're mainly gonna like whatever pickup you go with on these. EMG's are popular on these, or some of the over-wound offerings from Duncan or the other guys. We'd definitely recommend getting the budget models of these, and upgrading pickups. The hardware should be fine; most of these have Floyd Rose trems, which if that's the case, you're pretty much stuck with it. It's said that some Floyds are better than others, so that may be a mod to consider; a Floyd Rose by Floyd Rose might be better than the one on a $300 guitar. Some of these have really crappy vintage style trems that we'd recommend blocking them if you don't use them (or stop using them and block 'em anyway).
Cosmetic Mods: We've been seeing more and more cosmetic mods being done to guitars, and some are fairly noninvasive, while others are quite involved. Some Gretsch owners have used paint-pens and pinstripe tape to simulate F-hole binding, and these are hit or miss. It seems to depend on the care taken when modding. We've also seen some binding mods done to Gibson Les Paul Studios that simulate body binding, but involve removing finish. There are also inlay decals out there that are pretty convincing. When doing these mods, one must ask if they're doing it for stage appearance, or for themselves.
I had a guitarist that took an LTD EC1000QM and painted it white with a brush, then painted a black stripe on it to look like black binding. It looked great in pictures and on stage, but up close it was really disgusting. When on stage, people aren't always able to get a good look at the name on the headstock, but if the inlays are not trapezoids or blocks, and the guitar is supposed to be a Les Paul, people who know guitars are gonna notice. At the same time, I've never had anyone say a word about me using a Squier on stage.
Other simple cosmetic mods include changing out knobs, adding covers to open-coil humbuckers, and DR makes strings in every color of the rainbow... One can also swap chrome hardware for black or gold. Some guys leave the string ends uncut for looks, which drives me nuts. Not a mod, but still. It looks stupid.
Overall: We are definitely a fan of mods on guitars. We try not to get too weird, and the only time we mess with the wood of the guitars at all is when mounting locking tuners, and compensating for straplocks. Any experimental mods should be considered on budget guitars, and thankfully, the budget guitars are getting better and better at mimicking the big-dollar models (and better than in some cases). If you have ideas for a crazy mod, just Google it and you'll usually find a forum thread by someone else who had the same crazy-ass thought. Usually when it comes to off-the-wall concepts in general, we encourage them for comedy factor if nothing else. In guitars, we try to talk people out of really bad ideas, because guitars are like children to us.