So it all worked out in the end... changing a U class tkt to R class then upgrade from there. Change was GBP300, not too shabby.

New problem though... The CC agent upgrade my cabin with miles as I request, but she didn't collect the additional UK APD. The reissued ticket shows the original GBP 73 paid for LGWHKG route.

Is it likely they will try to collect later, or should I just chalk this up to good news?

Cheers,
Justin