Just so you know, it only prevents IP from increasing. You still get flagged by attacking others and you still need to hold control in order to attack players who are not flagged.
You'd need to make some pretty significant changes to the executables to allow normal maps to operate like Undo Stadium, where players don't need to be flagged in order to attack each other.
Or maybe someone could come up with a way of making it so players are autoflagged when entering a specific map and stay that way until they leave.