P 101 shorts around R103 increasing EQ'd positive feedback from the second stage to the first stage's cathode. P 102 allows this same signal - varied by R 103B to hit the same point after having been clipped by the "anti-parallel" diode pair. If you remove either of the optos the "other" opto gets slammed with a higher signal - if you remove both there's not one left to damage. If you carefully read the reference there is no "dire warning" <grin> of damage to the rest of the amp, just the optos.
Generally I like the the master volume V-4 that I've got as well as any master volume model and unless you really want a "distortion machine" with no need for pedals I'd recommend the older Ampeg circuit (see the other Ampeg post you responded to recently) - and perhaps the PCB would still be close enough to the earlier model to make modification less "painful." In any case the earlier model provides a better "starting point" for modifications.