I have a paper ticket, which was issued using 6 packets of coupons. I am not sure if this impacted the response or not, but the first time I tried to change dates on two flights with QF in Australia, the agent I spoke to on the phone couldn't find the ticket # and wouldn't change the dates without the proper ticket #. He suggested that I call AA's RTW desk. The AA agent (US based ) I talked to 15 minutes after the RTW desk closed couldn't help me as he said he "wasn't trained" in RTW issues.

Following Dave Noble's advice, I did succeed in changing it subject to a valid ticket coupon being presented at check-in.