First never EVER put a larger fuse in where a smaller fuse should be. If you do you may find that you burn up wires where you don’t want them burned up or worse you burn up an expensive control unit. The circuit breaker was an EXCELLENT idea and you earn big points for that.
As for the neutral switch that sucks. You could unplug it as you stated but you’ve already found the issue with that because you don’t have overdrive. Perhaps look for one in a salvage yard instead of buying new.