Lines like “She is not who you think she is” can be removed or given a new context to not feel weird. Also, lightning doesn’t inherently connect Rey with Palpatine. In fact, Rey used lightning in Trevorrow’s draft of IX, and she wasn’t a Palpatine in his version of the script. Again, it might seem like a Palpatine connection since we know the story leads there, but if you go into a Rey Nobody edit without those preconceptions, then it just would appear as an example of Rey tapping into her inner dark side.
A voice actor definitely won’t be essential, in my opinion. I think deleting and swapping out Kylo lines will be enough to make the Rey Nobody change work. Unless we want to make minor changes, like poppa and Hal having Kylo say “You were right.”