If you don't need/desire the dome light to come on when the drivers door is opened, just unscrew the button at the door and unplug it.

Or, if the buzzer is a problem for listening to the stereo with the door open, just wire the stereo to the the battery and not an keyed ignition source.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed