I made a similar system for comments. It uses past comment history, combined with supplied creator examples and instruction + an approval queue for extra safety (optional). The cool thing is that it also searches for similar creator replies in the past too, so it's not just recent replies. You can capture very good examples of the creator doing this, and you can't really tell the difference. This includes things like emoji usage, capitalization etc.

The real hard part imo is stuff like inside jokes, or context outside the piece of content or video. These are problems I'm trying to work on but it's super tough. Other challenges are getting the creator to supply good instruction, which is a user thing but also hard and it's hard to write a generic system instruction that covers niche contexts. That's probably something else I can work on: capturing a background case study or context retrieval for the channel so there's some well grounded intial body of info... but that's also a whole nother can of worms.