Parties are free to change a rule, but doing so carries risks, so the contract must spell out very clearly what the change is meant to achieve if unwelcome surprises are to be avoided. In particular, when the split of costs is changed, the parties should say plainly whether they also mean to move the delivery point and the point where risk passes to the buyer, because these are distinct matters.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.