Any Oneworld airline is able to reissue your ticket (some may not be very willing, esp. as there is no reissue fee for changes prior to flying the first segment). Using QF has 2 advantages: it is in their computer (other airlines will have to enter it segment by segment, including fare and tax calculation, so it takes an hour), and QF is able to print a large number of segments by computer (AA and CX are limited to 16 segments -- ticket must be hand-written if more than 16 segments). I think there is strong incentive to use QF to do the reissue. Never dealt with them in UK, but I've had good luck with QF reissuing tickets (issued by AA, btw) but that was in Australia. Others have reported problems with delays and strange RTW rule interpretations (presumably you are past that, as QF has already blessed your original routing and hopefully you aren't sneaking in some controversial changes).