Based on my test shot, I’d say replacing Sidious with Dooku is perfectly doable, so long as we can find a good enough voice impressionist for him. Also, the dialog introducing Darth Maul would need to be trimmed to leave out the part about him being his apprentice.
Still, I can’t help but wonder if it’d be too strange for Dooku to be hooded. Oh well, I guess.
Regarding the Darth Maul issue, would that mean cutting the scene with Maul and Sidious on Coruscant? Or just repurposing it? Because Sidious wouldn’t have had any establishing character moment before. Unless Dooku’s new dialogue mentions him or something.