I also think having AY as the ticketing carrier instead of BA comes close to AA in terms of taxes and fees. I purchased a DONE4 last week and by choosing the AY codeshare on the ARN-LHR flight, i saved SEK 5049, almost EURO 500.
All booked via OW online booking tool.
I am thinking of changing my itinerary later, after having used the first ARN-LHR flight and i suppose i need to contact the AY call centre for that?? Does anybody have experience with them? Knowledgeable agents? Please share your experiences. Thanks