BEagle, Yaqabi stores in Bahrein is an authorised Breitling regional dealer and repair agent. Theyt can replace the battery without invalidating the warranty. Wheras in the UK, they have to send the watch off to Switzerland with a quoted time of 4 to 6 weeks (Goldsmiths, Oxford) at three times the price. However, I'm not suprised that Breitling UK told you that having it done in Bahrein invalidated the warranty if they wanted the business.
I've had my Aerospace battery changed three times by authorised Breitling service agents in Bahrein (2 days), Dubai (3 days) and Hong Kong (3 hours). Each time it came back with a new gasket, a crown lubrication and having been pressure tested - and the most expensive servicing was about 22 quid (Dubai). And they have not had a problem unlike a mutual friend of ours who had his done in Switzerland and it filled with water the first time he went swimming. He was without it for 4 months.