Hi,
once you have gained Australian registration, you will have to renew it every year. This refers to Australian Physioboard standards, not NZ ones. Please refer to the Australian guidelines.
AHPRA - FAQ and Fact Sheets
If you wish though to keep your NZ registration, every year, you will need to undergo the process of recertification as per NZ Physioboard guidelines. But if you do not intend to ever work here, that might not be feasable.
Please also note, however, that you will have ticked the box on the NZ application form where you confirm the intend to actually work in NZ.....
Regards,
Fyzzio