if you have the original, unchanged, text file, you could simply a) stop the torrent on your pc, b) replace the changed text file, and then c) restart the torrent.
If you no longer have the unchanged text file, I BELIEVE, you'll need to re-do the entire torrent and direct everybody to save the show to the same directory that they saved the old version to. Fortunately, everybody who's already downloaded 99.8% of the old torrent would only need to download that portion of the "new" torrent that's different and would thus finish their download in a few minutes.