I have made some bookings originating from EU both via AA and BA, and so far (after both have ended published covid flexibility policy), and when the agent reads me the fate rules they are all changeable without penalty. However AA does restrict you to the currency of the ticket, so if it's euros you have more options than if it were to Hungarian florint or Swedish kronens. I don't know if BA has the same currency restrictions, although agent stated you can change the routing and previously BA has been pretty flexible in exchanging the various currencies at the daily rate 8n converting vouchers etc