only way i could imagine that would prevent well, editing of replays in such a way is encrypting the replay files in a encryption algorithm such as AES or DES then decrypt them when the client opens them, that way only the client could well, understand/read the replays and they'd be hard to edit. Problem with this is, doing something such as encrypting the replays would also block out people who do 'replay hacking' for the fun of it, such as adding "all joint booms" at the end of replays and other stuff like such.