Electrons

Except that protons aren't fundamental particles (the charge of a proton is made up from the individual charges of its quarks) and there are more particles that you seem to be forgetting. So what you're really asking is for the charges in ALL elementary particles to be redefined: quarks, leptons, bosons etc.

I think you're asking a lot.

That's irrelevant though. They didn't have to decide for each particle whether to call it positive or negative, they just noticed, "this charge is [some ratio] of [previously discovered particle], therefore it is [charge]".

Again, realistically I'm not asking anything. But all that would've needed to change is the arbitrary decision of a guy in the 18th century to write (-) instead of (+).