When I first watched RotS I thought that Sidious was only disguised as Palpatine (as in kill-and-replace) and the electrocution had just destroyed the disguise.
At what point did you think he was replaced?
I always thought the Clone Wars should’ve involved people getting replaced by cloned versions of them or something like that. But nope, the clones were just storm troopers. Oh well…
In-story, I think it would have already happened before the events of episode 1.
I don't know or remember when or why I started thinking that.
Your idea of clone replacements would have been a cool plot.