Fairly new to modding electronics, question about pups?

[Basstones71]

Hi -
I've done a bit of electronics work in guitars before but I've never experimented with my own circuits or whatever, always just gone straight froma wiring diagram. I have a Stingray knockoff, a 5-string, that I bought from RondoMusic almost 2 years ago. It plays nicely and I like the feel (and I only paid like $170 for it). Obviously not my main axe, I don't use the 5 strings as much. Anyway - it's been acting a bit wonky - sometimes notes will just pop out WAY louder than the rest of the notes that I had been playing, with no change in my style or anything. The pickup height seems ok, I checked/replaced the battery, still had the same problems. Took it in and they told me the pre was probably bad. Rondo, who has fantastic customer support, sent me a new one free of charge. They actually sent me an entirely new body of a the same model bass - chopped it off and sent the back half with the electronics and such. The shop replaced the pre and it's still doing the same thing. I kind of want to just make the bass passive and eliminate the preamp, because i'm ok with that. Since I have two pickups now, how difficult would it be to rout the body for a second pickup in HH config, and wire the bass for V/T V/T? It doesn't seem like that would be terribly difficult, but I'm not entirely sure and don't want to just dive in and screw up a perfectly good bass. If it would be easy enough, I'd like to add a series/parallel switch as well to kind of mix it up tonally. Any input is more than welcome. Thanks!