Mother Bear, thank you for your time and for the big HELLO! :)

Yes, you can renew the visa. Also, there are educational institutions which have an agreement with NZIS to offer course-length visas - however these are only available for renewals, not first application, so they are really 'remainder-of-course-length'.

But in case you hadn't guessed, my reason for wanting a visa for more than 12 months in the first instance is to avoid paying customs charges on some stuff I want to bring! If I have to pay up, then so be it, I'm not trying to circumvent the law, just want to know - and budget - sooner rather than later.