Yes. Each competitor must have an Australian Sailing number (or National Organisation number affiliated with World Sailing). There are a variety of great yacht clubs on Port Phillip that you can join.
If you don’t want to join a club permanently, you can purchase a Day Pass for the regatta from the RMYS office. Normally $20 per day has been packaged at $50 for the regatta. This cost is additional to the regatta entry fee.