This is actually something I've been wanting for a while, but never really got around to it.
You may know of MyBB's Split Posts mod tool - useful when a post is off-topic and should be split into another thread. However, I find that, at many times, users get off-topic half-way through a post, so simply splitting the post doesn't always seem right.
This plugin adds a new post moderation tool, allowing you to duplicate selected posts. If only one post is selected, you will be able to "dissect" the post (sorry, can't use the word "split"
). Dissecting a post basically makes copy/copies of it, but allows you to edit the message of each at the same time.
After you duplicate the posts, you can then split them