So after some research and consultation with a lab technician that I am friendly with, I believe I have an answer. If run on both a supply and a battery simultaneously, the battery would likely overheat, probably leak and maybe even explode a bit. It might also discharge through the power supply, burning it out. It probably wouldn't damage the circuitry of the pedal, aside from the physical damage and acidic mess which would result from the small explosion. In short, it is not a good idea, actually a very bad idea. Also realized that none of the connectors that I wanted to use are going to work because the stock jack has a pin shunt spring, and everything on the market is sleeve shunted. I tried Mouser and even called Switchcraft, but no dice. As of now, my pedal only runs on battery, but I am not ready to concede defeat. I have, (oh god) a plan!