Different voice tone, and Mask, and Chest plate for that matter… Only thing worth keeping consistent is the tint of Vader’s eyes. Almost impossible to fix the other stuff…
But why try to “fix” any of it? So his suit changes between films. It doesn’t break continuity for Vader to get upgrades.
I think it’s okay to manipulate some aspects of the performance to make the jump from shouty enforcer Vader to no-nonsense leader Vader less jarring and make the earlier iteration of the costume more in line with all the others as long as it’s subtle. You can still have the suit evolve without leaving the older versions looking unfinished in relation to the later ones. This is a special edition not a preservation of every aspect of the original film.
I may add this is the ESB:R thread and not the ANH:R thread so maybe the conversation should shift to there.