I just bought a covered Duncan Nazgul/Sentient set for my Schecter only to find that the pickup cavities are just a tiny bit too short (pickup lengthways, that is).

The guitar is an Omen Extreme 7, so it's not overly expensive and it already has a couple of battle scars (fighting with other guitars on a stand), but I want to protect the finish as much as possible, though I can hide my crimes somewhat under the mounting rings.

I have access to a dremel with a plunge router attachment and a small selection of bits, but that's basically it.

I'm thinking that if I mask off the top, then score the lacquer with a scalpel, it should crack away cleanly rather then flaking and causing issues.
After that, just go slowly with an end mill bit and square off the corners with a chisel.

I'm fairly experienced in general guitar maintenance and I've built a strat from parts, but I've never done anything as invasive as this.

Anyone got any tips or warnings?
Use a Dremel with a sand barrel (or whatever it's called) and just sand away until it fits.
My Soundcloud dudes
Recording gear:
Yahama Hs8
Saffire Pro 40
Shure Sm57
Shure Sm7b

Guitar gear :
Ebmm BFR7
Axe fx XL+
Walrus audio Janus
Ibanez Ergodyne
Black Market Custom cab
If all you need is to take of a little material, I would probably go for the chisel too. A good SHARP chisel will leave a nice smooth wall if used right, but you have to know how to use it. Keep the flat side up, NOT the sharpened bevel side. That won't dig in as much, the beveled side will dig in like crazy. It's for taking off lots of material in a hurry. The flat side, if the chisel is sharp, can be used without a hammer at all, and just scrape material off a little at a time. but it has to be very sharp...

Do not use a chisel with any gouges in the cutting edge.

Dremel with a sanding barrel will work, but it's hard to control it and get a smooth straight wall. I had to use a router, mine needed a lot of material to come off. In that case you cover the finish with masking tape or it will be scratched all to hell and back. I made a humbucker hole from a single coil cavity...Fortunately the pick guard covered my one big slip...
Hmmm...I wonder what this button does...