User blog comment:Dopp/Communicate Easily with Message Wall/@comment-1429792-20110926191935/@comment-1656630-20110926203202

Editable once they are made: yep, by the writer of the message, and by admins. (Also will be removable by message wall owner.)

The use case of vandals wiping their history pages is one we're making a high priority, and there will definitely be a way for at least admins (maybe everyone) to access that history.

Older Message Wall conversations will always be usable. If you really need something edited on an old Talk Page after the archiving happens, you can ask for that via Special:Contact.