You could certainly create an effect like that manually using the usual face morph software and techniques on each individual frame but it might start becoming a little tedious if there was no way to automate it. You could also just composite the fake at a lower opacity but obviously that just leaves you with two half transparent faces in the same place unless they were very similar to begin with. And yeah, it takes me about a week to train one up to a decent quality, and that’s assuming there’s plenty of source material of the new face to feed in, which probably isn’t the case for young Shaw since he was ROTS Anakin’s age in about 1930.