Apologies- I type this from a bustling hole in the wall eatery in BKK.

I just ticketed an exJP DONE3 at the old fares.

Details later, but here’s what worked for me- timeline in brackets:
1. book online with the first sector with CX (04Oct/~noon SIN). This makes it a CX ticket (at the QF fares, I think), and payment info is taken, but not charged. You have to call to get them to send a payment link.
2. call to change (regular line- I get a CX Diamond priority, but was still dumped to the MNL call Center)- do not pay- the call centre will see the ow website fare- I changed a DFW-BCN-MAD to a DFW-DOH-MAD
agent couldn’t process/figure out if it was allowed, sent to the manual pricing team (04Oct/~1400 SIN), supposedly on ‘Diamond Priority’
3. got an email with the required itinerary (05Oct/2120 SIN- it’s Saturday night in HKG!)
4. got a call that I missed (immediately after the above)
5. got a payment link that I paid through (10 mins after the above) with the CX filed fares.

The phone agent being unable to just make the change might have been the key.

etickets in the inbox, base fare of JPY 656,300/492,300 per Adult/Child.

A long post of gratitude to the regulars in this thread, and especially dvs7310 & of course pandaperth , with experiences with the engine, and a saga of mistakes, laziness, confidence with the first rtw (lack thereoff) etc will hopefully follow in the coming days (tight tax filing deadlines etc to be dealt with).