Beware of messing around with large systems! Your proposed "solution" will most likely backfire in ways you don't even imagine!
Then they do something really stupid.
Then they pay the price, and make their neighbor and children pay the price, saying "who could have known ?".
This is not only very arrogant, but also extremely ignorant of our history.
Rabbits are a non-native species what were recently introduced and are causing significant damage. It's very well understood what a NZ without rabbits would be like; it would be like the NZ that existed before rabbits. That's the point.
(And also like the smaller islands that are already rabbit free.)
The only similar species in New Zealand that it could spread to would be hares. If that did happen, that would be an added bonus. Hares are also considered a pest animal in New Zealand.
RHDV1 K5 is a strain of RHDV1. RHDV1 in all of its mutations only affects the European rabbit. As https://en.wikipedia.org/wiki/Rabbit_haemorrhagic_disease points out, it doesn't seem to affect other rabbits, like cottontails, black-tailed jackrabbits and volcano rabbits.
It also points out that birds, flies, rabbit fleas, and mosquitoes can spread the virus between rabbits, and those aren't "4 legged creatures."
The disease is endemic to most of Europe, so it's not like it doesn't have plenty of opportunities already.