Wouldn't it come down to proof of intent to exploit? Surely an actor who happens to look like Brad Pitt can't be prevented from working in the film industry on that basis alone? I agree that calling themselves Britt Pad or whatever might be crossing the line!
Seems like it is one thing to hire a look-alike of Brad Pitt (or your selected star), a very different thing to hire another actor and then replace his/her face with synthetic animated images of Brad Pitt.
The first would get laughed out of court. The latter would be an obvious ripoff to anyone (perhaps excepting some soverign-citizen-level pedants).
An interesting test would be a taking someone who looks extremely similar to Brad Pitt, but can’t act, and buying the rights to their likeness, and pasting it over an actor.
You could train the model on a lookalike and have him sign over rights to his (the lookalike's) likeness.
That’s why we can have fake Matt Damon (a.k.a. Jesse Plemons)