If a dispute arises between two users that cannot be resolved via normal communication, cast a custom moderator flag and explain the situation in detail, and a moderator will... moderate the dispute.
FWIW, code changes are a disputed topic. I feel pretty strongly that users really shouldn't be modifying other people's code at all, but some users feel it is OK if the person knows what their doing and makes their intent clear. Jeff Atwood always viewed Stack Overflow as a big source control system, and wasn't bothered by any form of collaborative editing.