If the corruption is reversible then the people doing the checking can also reverse it. They'll have both the corrupt version and the reverse-fixed version and just have to check an extra hash per thing they're scanning for
When the file is opened in a torrent client, it will recognize these changes, revert them (in memory) and seed the original file.
Not sure why you would go the route of having it predictable?
Even if that's not the case they'd just switch from grabbing a hash of the entire file to finding sub-hashes of the file or other fingerprints. You'd have to do a lot of corrupting to make this worth it.
If adobe premiere can sync my audio tracks when one is barely audible and the other has background noise you better believe there's a service that can find stored movies against a database of files
Also if you're already using BitTorrent why are you sharing these files on Dropbox et al
Your torrent client would see the normal file, they wouldn't see anything except random garbage.
Why? Um, perhaps to have a "torrent box" which stored data in a more accessible place?
Perhaps just to crap on someone's stupid censorship.