There isn’t currently a way to do that. Think of those posts as being messages, rather than being blog posts. When you write a blog post, you can make edits whenever you like, but when you send a message, once it is sent, it is sent.
You can however delete posts, so if you want to rewrite something, you can delete the old and create a new post. Be careful though, because when you delete a post, you delete any replies as well!
