As GM of a game, when I edit a post, there's a "bump" checkbox under the post.  I tried it and it doesn't bump a message up or down.  Perhaps bumping a post will bump its thread if bump control is on in a discussion board?

Normally an edit doesn't bump the thread.  By checking "bump" when editing a post you can force the thread to get bumped (not the message) when you make that particular edit.

And no, it does not override bump calming in discussion boards.