I've recently had very poor experiences with an RTW ticket (xONEx), where I had to make several changes to segments and dates during the trip, but it took multiple calls, hours on hold and then waiting many days to get changes made and the e-ticket reissued. In one instance, I missed out on getting on the flight I wanted because the booking class was no longer available after having to wait so long (3 weeks!) to get the ticket reissued.

In this case, the RTW ticket was originally booked with Cathay, and one of the main problems was not being able to speak directly to someone at CX who understands how to deal with RTW tickets. Everything had to be done through the first-line helpdesk agent, who then passed on the requests to another department. This meant lots of delays and waiting for callbacks which never happened, and lots of opportunities miscommunications.

I was thinking that for future bookings, it might be better to use a separate travel agent, such as American Express Travel, so I could simply email them with the changes I want, and they could update the booking and reissue the e-ticket directly.

Has anyone used Amex Travel (or other agents) for booking RTW tickets? Is it even possible?
And if so, does it work smoothly for dealing with mid-trip booking changes?