To fix a spelling mistake just type s/<old message>/<new message>
But this doesn't seem to work if the <old message> contains a slash.
Can the slash be escaped somehow? \/ does not seem to work.
Didn't find any other way then do changes before and after slash separately. If slash was not intended, then it's not possible to remove it.
Like you mentioned, slashes are one thing that the current "s///" replace behavior doesn't quite handle. We definitely want to improve the UX here in the future. There are a few public JIRA issues that have been borne from user suggestions - you can follow along at https://jira.atlassian.com/browse/HCPUB-1799 (watch/comment/vote) and you'll get notified of any improvements we make to message editing / deleting in the future.