Originally Posted by Steve M

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But this would work only if the transatlantic routing involved a city that both BA and AA served - otherwise, you'd need to add or drop a connecting segment, and this would require a reissue.



It was in my experience. Keeping the city pairs the same, but changing the carrier, was reservable without needing a ticket reissue. There was slight confusion at the airport as the ticket was not for the carrier I was flying and had not been endorsed to them (I was using an e-ticket), but it didn't need to be. Once a supervisor got involved, all was fine.