I'm sure this is more than you want to know, but we ended up changing our trip from October and in doing so it also changed the timing of our internal travels within New Zealand in that we were ending up on the South Island rather than in Auckland. The return flight was a paid flight in PE (outbound was a mileage award in business) and it was changeable for a $50 fee, but unfortunately that didn't allow me to change the routing. Cancelling and re-booking to a new routing from ZQN was subject to a $200 fee (times two). FWIW, the cost of two separate tickets was in the same ballpark as the cost of ZQN-AKL-LAX when I checked.

As it turned out, the website wouldn't allow me to change the dates on my own, so I had to call in and they let me change the dates on the flight for no charge--I think the agent took pity on me for being on hold for four hours.