I hadn't seen that. It contains lots of good information but I haven't been able to find change/reiisue fees on it. EDIT: actually, the fare rules are published on the long term fare list and says the following;

Voluntary change is permitted for NZ$50 per one way per person if it does not involve change of origin and/or destination
If it involves change of destination/origin, no downgrade permitted, new fare must be greater or equal to exchange, new fare based on:
If before travel commences: available fares at time of reissue
After travel commences: avaible fares at time the ticket was originally issued.

To me, this means it should cost $50 + the difference between an ORD-LAX-AKL and a LAX-AKL fare. But maybe more experienced travellers know more about this.

Thanks for this, it was quite helpful.