Neither IB nor AA is obligated to do this and it is IB as the ticketing carrier which will handle the transaction.

I would suggest calling IB immediately. Have the new proposal ready, along with flight numbers, and ask the agent to reissue the tickets. IB may not be particularly helpful here and tell you that you will need to cancel and rebook, but you have lost nothing by asking.

Also worth noting that if the PHX-TUS segments are not convenient, that this is a <2 hour drive and, depending on where you are headed in Tucson, may be even less. Worth considering to avoid a micro-hop + connection.