Originally Posted by
anabolism
They should be able to. In years past, there were sometimes barriers in that when the PNR was originally created in a GDS other than SABRE (e.g., created by QF or CX or a TA), often AA couldn't see all the segments, which prevented them from taking it over. I don't believe that's still an issue, but I haven't personally tested it.
Amadeus to Sabre transition should be possible, but there is still sometimes system incompatibility issues. In my case, AA wasn't able to see original taxes paid for booking that was created by QF, so AA rating desk didn't agreed to make changes for me even that AA RTW desk was willing to help.
There have been also many reports that it works as it should.
SFO_FT, you should ask AA RTW desk directly, if they can do changes for you. Hard to say in advance if the system works for particular booking for sure.