Re: Quick question about moving messages within threads.
Another possible option...
You could have a thread that is a notice (so it will always stay at the top of the game thread lists), and keep your 'latest message' as the message visible there...when you needed to update/replace the message, you could copy it into an archive thread (not to be confused with an ARCHIVED thread). That way, people could go back and read older messages, if needed.
But, really, there's no need to keep the newest post on top. Just get your players in the habit of clicking the 'new' or 'last' link from the game menu listing for the thread (most of them already are, anyway). It will accomplish the same function...click on 'last', you go to the most recent post in the thread, which also happens to be the last post.
So, there's already a pretty simple workaround in place...