I used a Northwest Visa mileage discount code (6000 miles discount) to book an award ticket that I would now like to re-schedule. If I try to re-book the flight on-line the new booking does not include the discount and I have to pony up 6000 additional miles to make the change. The reservations desk tells me that these are one time use codes. Any ideas if it is possible to change my award ticket reservation with the mileage discount? Thanks