Can characters be renamed?
Interesting question ...
LonePaladin's mileage is how it was intended to work - Fred the Fighter might become Sir Frederick ... and then has his knighthood revoked so he's back to Fred again ... behind the scenes, I'm guessing that because it's all under the one character ID the player has edit access to the older posts - as far as the code's concerned you're just posting as that character ID, no matter what name is currently hanging off it.
Now, I've just had a bit of an experiment and I was able to add an NPC and two characters to different players, all with the same name so a) there's no error trap on identical names, and b) they should all be able to post as that character ...
... but per my speculations above, I'm guessing each player's "Joe" would have a different character ID attached, so while they'd be able to edit their own post (under their Joe's character ID) they probably won't be able to edit posts made as Joe by other players (using their respective character IDs). Which probably doesn't matter anyway. :>