If you stuck with just adding new dialogue to the hologram scene, you could have Palpatine say something like:

Soon, I will have a stronger vessel.
or
Soon, my spirit will have a more worthy host.

It could be a way to address the question of, “Why would Palpatine tell them something that would make them want to kill him less?” It’s like, Rey probably would’ve killed you before you told her that. Yes, I think he tells her because of his hubris and sees that there is no other way (until there is), but it would alleviate that question if the audience could learn about his plans for spirit transfer while he tells a confidant of his intentions.

Also, everyone would probably know he is talking about Rey here, but it is still vague. He could be referring to a new clone body. But then on Exegol when he says, “That is what I want” it would confirm it is Rey.