I'm being a bit lazy here but I haven't managed to find an answer in the documentation I've found so far, so I'm straight out asking for help
I want to make a styler-type add-in that puts each sentence on a new line within the text sections of an RMarkdown file, probably by doing a find and replace on ". " ... you get the picture. But it wouldn't be a good idea to apply that find and replace to R code!
I don't think so, you probably have to detect it yourself. We do this in styler. On the other hand, I know it's not quite what you asked for but you could also have a look at https://github.com/lorenzwalthert/stylermd that prettifies markdown.