Since you are a DM, you should just call the MPO Centre, ask them to change the booking in CUPID for you. If the Tkt No is not getting through then just take note of it, on the day of travel just tell the ticket agent yout txt no.

Problem is that CX does not have RTW desk (as RTW products are not as popular in HKG compare to other cities) so many CSO does not know the rules.

Alternatively just ask the MPO centre CSO to make a reservation for you on AA and tell them u will provide the ticket no later.
Then call back for another agent and provide them with the ticket no.