All that has happened is that AA has auto-rebooked OP. He is free to call in and request something else if he can find it. Award inventory won't matter between AA & BA on that route, but as others note, I'm not seeing Y inventory on either AA or BA.
OP is certainly free to cancel for a full refund and then rebook whatever he wants. But, I would advise having the other flights in hand as the IRROPS will affect things for a good long while.
Key here is to call AA ASAP.