i would agree with quebec.

although the problem with booking a D segment is difficult because i believe you already used up your transcont sector.

(opinion only, again)
however, i believe you can specify your 7th segment. i.e. if you have 'flown' the transcont. you can re-issue your flight (with your new sector in A, and teh transcont in D). and you speficy the 7th segment as teh D sector.
later, (afetr re-issuance), you can rebook into a 2 class flight.

as otehrs have said, AA is notorious at re-booking RTW. so better have your re-issuance (and PNR) with CX/BA, adn hence also your later rebooking