Well, I'm not sure I understand your problem now. The built-in DHT patch in that version of Serenity works fine for all newly-added torrents, and the mod I posted before was able to unlock DHT for pre-existing ones. Neither of them modify the .torrent files, so the info_hash shouldn't change.
For the record, does the attached mod do what you want? (It's the official uTorrent 2.0.4 build 22150 with all private flag checks bypassed and nothing else)