Meh. You are in no way responsible for making others behave ethically. Put whatever sticker wherever you like. Don't be a lying d-bag when you sell the instrument. If the person you sell it to wants to be shady, that's on them.
Honestly, the argument to not put a decal on it because it is unethical holds about as much water as arguing that using a replacement neck with the Fender headstock design is unethical because someone might think it is a Fender due to that headstock. Ma. Larkey.
edit: When I've replaced necks in the past I've not bothered with putting a new decal on because I just don't care enough to bother with it. It isn't unethical however.
interesting opinion regarding ethics. there is a parallel in the world of car collecting. some people create 'clones' of their favorite vintage cars using reproduction or counterfeit parts. they then sell the vehicle, claiming it to be a non-original 'clone'. a subsequent owner sells the 'clone' as an original. someone is defrauded and sues for damages. the person who did the original 'clone' modifications is held to be legally liable for part of the damages.
the current defense against this sort of liability is a notarized paper trail stating a 'clone' is such when sold.