Change iOS file suffix?

I compile my web articles as plain text, because if I turn on the Markdown toggles, Scrivener/iOS comments out all my YAML headers. That’s not as helpful as it might be, but life is tough.

I renamed the top folder to index, so that the output saved file after compile will be named index … but I need it to be named index.md, not index.txt. I can edit it, and suffer the prompt about being sure, of course.

But … is there a way to tell Scrivener that I’d like my output files to be of type md rather than txt, once and for all?

Or … some different flow from what I’m using?

Thanks!