Air New Zealand Air Points - Changing flights for domestic sector on international itinerary

I'm flying LHR-WLG in mid-July (NZ1-NZ5-NZ411). It's a Premium Economy Global Flexi Fare, with the domestic sector booked into Y class.

I want to change the domestic sector to take an evening flight instead and spend the day in Auckland. Does anyone know how I can do this easily? Is there a way to do it online, or is it required to call Air NZ and put up with a $60 service fee?

I do see that domestic flexi fares can be changed at the airport on the day of travel. Does this also apply to a situation like mine (domestic sector booked in Y on an international itinerary)?

I'm flying LHR-WLG in mid-July (NZ1-NZ5-NZ411). It's a Premium Economy Global Flexi Fare, with the domestic sector booked into Y class.

I want to change the domestic sector to take an evening flight instead and spend the day in Auckland. Does anyone know how I can do this easily? Is there a way to do it online, or is it required to call Air NZ and put up with a $60 service fee?

I do see that domestic flexi fares can be changed at the airport on the day of travel. Does this also apply to a situation like mine (domestic sector booked in Y on an international itinerary)?

I have only changed business saver domestic legs which are about as restrictive as savers. The domestic leg can be changed over the phone for the usual call centre charge or can be changed in lounge on day of departure for no charge.

I'm flying LHR-WLG in mid-July (NZ1-NZ5-NZ411). It's a Premium Economy Global Flexi Fare, with the domestic sector booked into Y class.

I want to change the domestic sector to take an evening flight instead and spend the day in Auckland. Does anyone know how I can do this easily? Is there a way to do it online, or is it required to call Air NZ and put up with a $60 service fee?

I do see that domestic flexi fares can be changed at the airport on the day of travel. Does this also apply to a situation like mine (domestic sector booked in Y on an international itinerary)?

I don't see why it wouldn't apply to you. If you do have a flexi fare, I'm sure it'd flow through to the domestic flight and if there's room on an earlier flight, you would be able to change it. Either way, the people at the domestic transfer counter at the international airport are usually quite nice and should be able to help..
But maybe there's someone who has evidence that it's doable.

If it is booked in Y then it is fully flexible and you can change on the day for free, provided seats are available AFAIK.

You might (should) be able to do it online, but you'd pay the $50 fee.