Obviously special effects was bound to go this direction, and that would almost certainly be legal with or without actor permission. Replacing a computer mildly attended by a human with another computer mildly attended by a (much less paid) human is so common as to attract practically no notice. Programming explosions was always a job with a shelf life. Either the production can afford real (if scaled down) pyrotechnics and practical effects, or they're a no-budget indie production that would otherwise go with some stock library for the purpose. So that gets AI into machines and onto desktops very quietly and legitimately.
Also, it's still acceptable to use AI to produce storyboard images and placeholder music and the like that are never going to see the light of day, right? I imagine the writers throw their scene into an AI and let it churn a few iterations. If none of them are even close to what they want, send it off to a sketch artist like always. Otherwise it may be faster and involve a lot less message-passing to just fake it themselves and explain/caption how it's wrong. They already do this when a scene changes after sketches have been made. Again this gets it into machines and onto desktops. It allows for a plausible sounding excuse of "there aren't any clean systems, every editing rig uses AI for in-house purposes". Render rigs make half-decent AI rigs too, even if they're not designed for that purpose. The builds are very, very similar -- GPUs, RAM, storage, and to a lesser extent the CPU itself are all pushed to 100% at some point in both workflows. A pair of 48 GB RTX 4090 is great and all, but you need the bandwidth on the system side to feed it and to display/store the results.
The questions start when the material designed for in-house use gets disseminated to the world, as it might be for a trailer of a movie still in early production. But if they haven't even hired a cast yet, they're not contractually obligated not to use something resembling a known actor -- although they may burn bridges if it ends up they want that person for the real deal. I suppose if they said "do it in Ghibli style" then nobody could claim to be fooled that it actually is Famous Actor.