Do criminal defendants ever legally change their names before trial so the conviction is under the name of the witness who outed them?

I'm pretty sure (at least in the US) you need a judge to sign off on letting you change your name. I would guess most judges aren't going to find "trolling my accuser because I think I'm going to lose a trial" a valid reason to change your name.

Probably not because it wouldn't accomplish anything.

Life is not a video game.

Or bad fanfic.