In Victoria, the Medical Treatment Act (1988) allows a patient to write a ‘refusal of treatment’ certificate, but only for a current illness, and the illness need not be terminal.
The Certificate is available for down load from HERE.
The Medical Treatment (Enduring Power of Attorney) Act (1990) also allows for the appointment of an Agent or Proxy, while the Medical Treatment (Agents) Act (1992) allows for the appointment of an alternative agent as well.
There is a helpful Enduring Power of Attorney (Medical) Fact Sheet available for download HERE.
The Certificate for the appointment is available for download HERE.