Maybe I’m missing something, but why is Palpatine lying about being Rey’s grandfather necessary in the first place? It’s not like a massive amount of runtime gets cut if you remove all lines where Palpatine mentions this: depending on how you rewrite the hangar reveal, you can even keep some lines that were originally meant to allude to it. Personally, I think it would be much more effective if whatever reveal Rey gets about her past is actually true, rather than just a blatant lie that Rey can overcome by simply finding out it was a lie in the first place.

Jar Jar Bricks’s idea of Rey being a clone is one of the most promising alternate reveals I’ve seen proposed so far (especially given you need to cut practically nothing), but I think one of your earlier ideas, where Rey was trained by Palpatine as a child, still has a lot of potential. It makes both Rey and her parents unambiguous “nobodies” (by blood, at least), while still giving Rey a strong connection to Palpatine. If anything, I actually think Rey having spent a significant portion of her early life with Palpatine is a much stronger reason for her to feel drawn to the throne than “evil genetics” or whatever.