My 2 cents on the whole "shifting gears is illegal" thing: the SBP shift kit is a crank assist device. It does not have shiftable gears.
The shiftable gears are part of the bicycle and are independent of the engine system. It's a shiftable bicycle with engine on or off.
If you had a shiftable jackshaft, now maybe that's different. I have never heard of anyone getting in trouble just for a shift kit.