cant you leave it ZK reged and then you woundnt have to pay any duty etc on it, and with the trans tasman agreement any one can over here can fly it with a basic licence conversion.. Vincent Aviation and the Toll 737s have ZK regd aircraft operating in OZ..
I don't believe you need the licence conversion, (I never did anyway) but the aircraft has to be maintained to the NZ standard and by NZ approved workshops, unless that's changed as well.