Set up the change with BA on the phone and they can do a reissue pretty much anywhere. I did one at SEA last year - got to the airport right when the counter opened (no crowds yet) and they did the reissue in about 40 minutes, 20 of which were spent with them trying to fix a printer that had gone tango. In the meantime I got clued in on lots of cool BA gossip (which has turned out to be largely wrong, BTW.)