As I understand it you are supposed to turn it in at expiration. Not sure about location, someone said it had to be retruned at the location it was purchased but ?? I guess you can just reapply for a new one when you turn in the expiring one. If you are going north close to the expiration date I would think you could just stop on the way up and cancel it, then simply apply for one when you come back down. None of this appears to be computerized, at least at Sonoyta and it seems they have no way to know much. You are only supposed to have one but a friend, for whatever reason, applied for and was issued an FMM while holding a valid FM2. Another person had an expired FM3 that was not cancelled but was issued an FMM.