Originally Posted by
KARFA
No this wouldn't work. As soon as you merge it in to the existing LHR-HKG it will be repriced as a LHR-HKG-LHR booking with normal taxes/fees/charges. The no-YQ is only possible for exHKG bookings so would be ok if you did LHR-HKG and HKG-LHR as one ways, but obviously you can't do that with a 2-4-1.
CWS's post and
cbagent's contribution to the wiki imply that the bookings are never actually merged, so the inbound leg remains ex-HKG. Seemingly there's only a half-avios repricing, not a cash repricing.