you must also pay a fare difference as well. An M fare is fully flexible, with no change fee, however they want a fare difference of 400 dollars for me to change my routing to YUL - YYZ - YVR - HKG instead of the current YUL - YVR - HKG that I am booked on. To me that is not a flexible ticket at all, I still view it as a 400 dollar change fee.