What I usually do (might be the dumb thing) is to delete the post (usually typos or I forgot to put something or something equally stupid) and then re-post after cleaning or adding it up. I do wish there was an edit post but do understand that it would need some sort of patching of messages and could quickly be convulated for pod admins.
I have no idea when I do delete posts, are the posts eventually removed from other federated network (within the diaspora fold at least) or do they remain forever ?