All you have to do is prompt your AI with a writing sample. I generally give it something I wrote from my blog. It still doesn't write like I do and it seems to take more than that to get rid of the emdashes, but it at least kicks it out of "default LLM" and is generally an improvement.

It's fine. We can't have it both ways. I prefer bad grammar to Claude blandness, so I think the author should just write how they write.