I just pushed out a bunch of changes for editing messages. If the group or user is moderated, the edit will need to be approved, just like a pending message. When editing a message, you can add a note indicating why you're doing the edit, and you can view different revisions of a message, just like a wiki page. Also, when a message is edited (and approved if needed), it is sent out to the group again. Finally, when editing a thread, you can edit the hashtags that are applied to the thread, by editing the subject line and adding/removing hashtags there (I'll eventually make this nicer, but it works for now). A couple bugs around manipulating messages have also been squashed.
To accomplish all this, I had to make some rather large changes to the code base (it was a couple weeks worth of work). I generally like to do things in small chunks, because any bugs are generally quickly found and of small importance. But I couldn't do that in this case. So, while I have tested the code a lot, I'm a little more nervous than normal.
As usual, please let me know if you see any issues.