I thought for a second that the commissioner changed the money distribution towards the winners, I guess he can't
Hmmm... When did he make that post?? If you can still see a post made from the beginning of the season, then there mustn't be much of any trash talking in your league.
Remember, while he cannot edit a post, he can always delete an old one and post a new one. Just make sure there's not discrepancy in the order of posts (and their message #s).