Recently, on a trip from SYD- AKL, I decided to change to a later flight. I was originally booked on an A321neo - Works Deluxe
The check in staff made a phone call and moved me (free of charge) to PE on the last flight out of SYD which was a 777 - it was wide open in both PE and J.
I did enquire about change fees and the very friendly check in agent replied she waived the change fee as a gesture of good will.
So I did not end up paying anything for moving flights and I was extremely chuffed about that
And cos I felt silly, I used 150 APD to move up to J on that flight but was charged 30 APD on top as service fee since I did it at the counter.
Good result overall.