Sublet, I'm not sure it's as easy as reversing the function of the push/pull. I'd imagine when the pot is pulled out, it's opens the power circuit. It may be possible to install a micro switch/toggle in series with that circuit to allow you to do the same thing. As another option, maybe using a TRS ( Stereo type 1/4" ) plug at the Instrument end of the cable without the "Ring" being tied to the "Tip" or " Shield" terminals. Worth a quick test at least to ensure you get a signal from the instrument. If that works, you won't need to modify the bass, just change the cable the other 5% of time. Certainly worth the test however.
Or you could take the knob off and put a rubber grommet under it so it won't push down.


