You should be able to re-route your ticket with a 75$ charge as you wish, with a stopover in HKG. Be careful in chosing which flight to take for NRT-HKG, some flights are CY configured. HKG-AKL is most likely 343, therefore you won't have the Betsy full flat seats. If you want the Betsy seats you should fly on the 744 to Sydney first, and then connect with QF. Although in my opinion, the 343 conventional first class seats are comfortable enough.