That doesn't mean anything legally either. It's not like you give up your electors when you concede. It's just part of losing gracefully. Technically the only thing that matters is what the electors decide to do.
Well... there is such a thing in law as estoppel. It's primarily used in a civil context; I'm not sure a situation has ever come up for it to be tested in election law.
I severely doubt that someone would non-anonymously choose to be the single person that gave away the election to their declared opponent, weeks after being a loyal partisan.
If there's one thing I don't doubt, it's people's dedication to a president they believe is the only person fighting the 'deep state' and other things along those lines. I can easily see it spun (or justified) as "defending democracy" rather than upending it.
