You need to understand that system wise, DL123 operated by AF456 is not the same as AF456. You're booked on a DL flight, not AF. Therefore you're limited to what DL is selling for their flight. Now since the flight is operated by AF, information is sent over to them, but they have no control to change it. The information is just being fed over to prevent AF from over booking their flight number that actually operates the flight. Just before DoD AF takes control and can make changes.