Only one of my four bass guitars are modified, one is rebuilt...
The modified one is my P-bass based B.C. Rich Ironbird. I replaced the original pole pieces from the pickup and replaced them with a set of Aluminum Oxide cap screws from a cheaper version of the Seymour Duncan Invader. This was to enhance the bass frequencies as the split pickup in that bass is backwards from the usual layout.
My 80's Segovia is unmodified, but does have much of the electronics replaced, and I plan to get a suitable replacement neck for it at some time this year as the original is warped but tolerable, and replace the bridge while I'm at it since the low E string saddle is seized out of whack.
My Epiphone EB-0...I want to modify it, but I need to procure another "Mudbucker" to do what I want, which is install a second Mudbucker in the bridge position, and add standard SG style wiring to it.
The Mustang, that's staying STOCK. I love that thing as it is and it's taken over as my main bass.