Sure you can, though I stumbled on it. Type s/sub/repl and it edits.
HipChat works with Pidgin, which doesn't support edits, I imagine you'll see something similar as with the Discord edit feature when you're connected via Pidgin (you get a new message, prefixed with EDIT:).
You cannot edit comments in Hipchat. I can talk about other issues as well but not editing comments is a deal breaker for me.