There's a high chance you'll go try to vote as someone who simply didn't register. In California you could then register as that person and vote provisionally, but polling officials will check your identification.

Alternatively you may attempt to impersonate someone using vote by mail. In that case, there won't be a ballot to vote at the polling station, and even if you are able to successfully register provisionally or convince polling workers to give you a blank to fill out, election officials are already looking for these kinds of duplicates.