[bruce]

Maybe there is a way to modify the switch assembly so that when you're depressing the trigger to shoot semi, it'll come in contact with a wire contact that is set for a 9.6V. Pulling it further back will let the switch contact a separate wire contact that will be set for a 8.4V. You'll have to run an additional wire from the battery pact to give you the 2 different voltages of 8.4V for lower RoF and a 9.6V for the boost in reducing trigger lag time. The second wire will be soldered to the seventh cell.

I'm not sure if it'll work because I don't have a P90 anymore but in principle, it could work.