So, on one hand, Cole's fight leads me to believe that level 4 evolutions work in a similar way to One Piece's awakaned devil fruits, in that they "externalize" powers that are mostly internal and individual. Which leads me to believe that once MC evolves, he could perhaps alter the form of other people and things as well as his own... and maybe alter memories as well which would be fucked up and maybe reserved for 5. This could mean that he could help Liz and Amber separate once more.
Now, on the other hand, the fact that WW explicitly gave Liz and Amber a way to switch between one another, and hinted at them eventually being able to do it without the earring during the Shopkeeper interaction, also kinda leads me to believe that the twins' change is permanent, or at least long term. Either this means that I'm talking out of my ass and the level 4 transformation will evolve MC's powers in some other way, that even if he does evolve in such a way he won't be able to revert Tanos' procedure, or that we're a long, long way from a new evolution.
Or maybe something else entirely, I'm just speculating. Game's great though.