The flights are slowly moving over from bmi to ba flight codes. Take Vienna for example. That was a bmi flight using a bd flight number. It is now a ba flight using a ba flight number. The aircraft and crew are still bmi so other than a flight number you should not really notice any change. It will still arrive into T1 so wont affect your connection. Its worth noting the bmi summer program is running as planned so time should also remain the same. Hope this helps