As long as you cite the dialogue, and it's an actual rewrite, that's allowable. There is plenty of that throughout the archive. What we're talking about is where someone takes a script and uses it verbatim, maybe changes the character names. No retelling of the episode from a different perspective, but just posting up the episode as their own work.
The same applies to an actual "read-the-book". Those are stories where an author usually puts a sentence or two of a character saying something or another, and then copies the actual book content verbatim, as the character reading the book to someone in their story. That's obviously NOT acceptable, nor is it a new spin on the book.
When I, or any other staff member, as an example; searches the text of such a story, and it comes up with 0% original content for the bulk, and links to a copy of the script in question, there is an obvious problem.
We're all certainly aware that some archives actually allow this, but many more of them do not, as it is still plagiarism. Taking a story and making the majority of it a copy/paste of a script/screenplay/book, is just what it sounds like, copypasta plagiarism.