Okay, I have passive pups, and a preamp. Is it possible to wire the passive pups so that I don't have to use the active preamp, just like normal passive pups?
If you're wiring around the pre-amp permanently, you could just plain remove it, and add a tone control in one of the empty spots in the control cavity.
As far as the volume drop, just turn your amp up a little bit.
No. I have a G&L that has a passive treble and bass control. A passive tone control is cut only, no boost. But it means when you switch from preamp to passive, the tone controls still work.
But I assume the tone controls are treble, mid and bass. A passive mid tone control tends to attenuate the signal too much.
Why do you want to bypass the preamp? If you want to do it a lot, you could always get an EQ pedal.