Hi Tarmac,
What you've expressed there is a common fear of a CVD individual, as some countries do require some kind of colour assessment at renewals, which really does suck! (yes that is a technical term lol) Currently in the UK, we are not re-tested at renewals, as sensibly our deficiencies are deemed to be congenital and with us for life, which obviously is the case. In the States, they test at renewals, but if you have been succesful, you will have evidence of your success to present to the AME. I'm sorry but i really don't know the regulations in NZ, but I understand they are one of the less tolerant countries in this area. Best of luck with it mate.