So if the upgrade of the whole ticket is treated as a re-issue, would getting this done at the airport on day of departure (1) be possible given that a complex process may be greeted with a "can't do it, go to the city office" answer; (2) would the advance purchase requirements kick in and so stopping you leaving immediately after the ticket change for 7 days or whatever, and (3) could this be problematic for a last minute change and actually getting a seat since they may have been given to upgraders?