Yes - trying to do this without getting the ticket reissued is very risky. But as number_6 says, you might well be able to persuade a BA ticketing desk to reroute/reissue it without a change fee since there is very little work in this (no change to fare basis etc.). BA T4 at Heathrow might be worth a try if you are passing that way - I hav ehad good experience there, and reports suggest that T1 ticketing is less clued-up on ONE tickets.