Originally Posted by mrcimino1

If they allow a change to another co-terminal on day of flight, with no additional fare, then that is good. However, since MSP-JFK fares have been considerably less than MSP-LGA fares (due to Sun Country competition to/from JFK) I don't think you could ever change it any earlier. Even though they are listed as co-terminals, when there are "airport specific" fares the change would not be allowed prior to the day of flight.