I think of furries and other online friends like this, yes. Being trans isn’t the only situation in which one has chosen an identity other than the one they were assigned.

That said, I wouldn’t characterize Vegeta as deadnaming Goku exactly. I can’t recall that Goku is upset by it, and I think it’s mostly there to indicate Vegeta’s continued connection to his home planet even after many years of being an Earthling.

Calling Steven his mom’s name is deadnaming.

I think the usage there isn’t meant to be correct, but incorrect as a joke. It’s like how I’ve seen people call themselves a tran. (Trans is obviously plural.)