As per what PCX said.
If you already have the Oz licence issued, the NZ licence and currency thereof has no further bearing on it. Though I would be interested to see if you can talk CASA into letting you do just a normal Oz IR renewal as opposed to an IR Initial on the basis of another licence. (This is what JAR/EASA allow)
Also see if you can save some pennies using a sim. You didn't say what aircraft you are using. I see this newly operating
sim can do Multi Piston and is certified to be used for renewals.