Rule 240 must be similar to another rule that applied to a friend of mine. He was flying ORD-LHR via MSP on NW.
His flight out of ORD was delayed or cancelled. NW wanted to route him to LHR in some other way. This was unacceptable since he had a business meeting the following morning that he would miss.

The guy called his travel agent and was given
instructions to demand that NW route him through JFK and put him on a BA Concorde flight (at NW's expense of course.) When the NW supervisor refused and said he had to do it their way, he followed the travel agent's instructions by saying "that's involuntary routing." The NW supervisor was very agitated
and literally threw the Concorde ticket at him! I guess a good travel agent can really pay off.