It might be hard to shape the right dialogue (you should look into those voice emulator AI programs, I know there are open source versions of it, or find a good Adam Driver impressionist maybe)…
I can do the audio engineering into 5.1 surround as well as the impression and voice using proximity effect into the mic. Cranking up the distortion just slightly can help mask the fact it’s not the same voice actor. No matter who does the Kylo “impression” or how well they do it, it will sound a bit different and the sound engineering will be at best slightly different. Which is why any one scene with any changed Kylo dialogue will likely have to be completely re-VO’d even with dialogue which stays the same. Punching in/out between different actors/sound techs will be too noticeable.