Yes it would come up differently but the amount of time, money and effort they'd have to put in to catch every piece of contraband that comes into New Zealand just makes scanning all the packages that come in too unrealistic.
Just had a read through this thread and I'm actually quite disgusted by some member's disregard for this country's laws. Sure, you might think they're silly cause you can't get a slightly different fish or a prettier looking plant like the rest of the world, but believe it or not, they're here for a reason. Unless you've tested such plants and fish in a sample of New Zealand stream, who are you to say whether they will thrive or not? Is getting the latest fish or plant, an international hype that will have died down in half a year anyway, really worth risking the truly unique and beautiful ecosystem, flora and fauna we have here in New Zealand? If your answer is yes then you really need to rethink your residency in this country.
TL;DR: The laws are here for a reason, get out of the country if you can't follow them.