When AA has a schedule change on an AA marketed flight (regardless of operating carrier) more than 24 hours outside of departure, AA will automatically transfer the passenger to the next available flight.

Below are 5 different scenarios explaining on what to do with the original e ticket:

Time/Flight number change only on AA flights, either on 001 or other airlines ticket stock
no need to have the ticket reissued or revalidated, the customer can check in using the original ticket number. Travel agent can print out a copy of the new flight number and/or timings of the flight.

Routing change AA ticket with only AA flights
Travel agent reissues the ticket adding ‘AA SKED CHG’ in the endorsement box and an OSI to AA ‘AA INVOL SKED CHG/AA FLIGHT NUMBER/DATE/CXLD OR SKED CHG

Routing change AA ticket with AA and other airline flights issued on the same ticket
Travel agent needs to contact AA to advise ticket needs to be reissued, AA will reissue the entire ticket 3 days prior to departure of the schedule changed flight.

Routing change other airline ticket stock
Travel agent needs to contact AA to advise ticket needs to be reissued, AA will reissue the ticket 3 days prior to departure of the schedule changed flight. AA will only reissue the AA coupon that was affected by the schedule change.

Schedule changes within 24 hours
contact operating carrier.