Sydfly, I have successfully pre-allocated exit row seats on NZ as a UA *Silver. Call and ask - you shouldn't have any problem, unless of course they have already been allocated which is quite likely.
globeflyerca, Koru Flyer was referring to the change in NZ's domestic services to a 'low-frills' model (single class; meals replaced by tea/coffee and cookies) effective from a few days ago. No changes to the (excellent) international services.