You can't change anything in the torrent. The torrent has a hash (security check) that will give you an error if anything is changed in the files of the torrent.
So, what you could do is…
1: Stop & delete the torrent. Un-archive the files and do what you like.
2: Keep the torrent running. Copy all the files of the torrent to a new location and un-archive the files and do what you want.
If you have already un-archived the files then you might be able to stop the torrent put the files back and try to re-check it. It could possibly fail, but it might work. I've never tried it.
Best of luck,
desioner