OK, that helps. From your description, it seems like something that should happen automatically and possibly be a trait and not an action. This makes it more powerful, but also easier to define CR wise. Maybe:hehe yeah this is the difficulty of translating a protaganist from a full story into a monster
For the Fate Shaper, effectively think of it as the old multi-verse idea. The Fate Shaper has an infinite well of them to draw from, so he can easily just switch to one where he zigged instead of zagged, and didn't take all that nasty damage from before. In effect, constantly replacing himself with another version of himself.
That said, even in my story there is a limit to how often he can do this (in the story he is actually drawing from his own soul...and so like any muscle it gets tired if you use it too often). So perhaps I could just put a simple 2/rest cap on it, to ensure it never goes completely nuts.
Reform Shelf (2/Rest). If the Fate Shaper is reduced to 0 hit points, it doesn’t die or fall unconscious. Instead it pulls a new body from an alternate reality (no action), all conditions and effects it is suffering end for it, and it regains 200 hit points,
I realize this probably blows your CR budget, but it it seems to fit what you describe better. This guys are so unique I would suggest making them what you want and just seeing where the CR chips fall. You can of course adjust that based on how many HP it has and how many it recovers with Reform Self.
However, please note that both your and my version of Reform Self could fall victim to Chill Touch. If you want to prevent that, perhaps cantrip immunity, which I have used before.