I've locked the player name change feature, and made a button to unlock it
Can't see warranty of what is this. Why did you block this feature only instead of disabling saving at all? Why distributing certain replays (edited or not) under different usernames would be more injurious than openly cheating just my own results?
All right, maybe one person per thousand would have enough patience to misuse this tool as-is, still... I'm not sure about this approach. We already have some non-dangerous replay viewers.