You do not need to register with NICNAS if you only make soaps in Australia without a chemical reaction by mixing or blending ingredients purchased from an Australian supplier.

What is mixing and blending?

Using products such as soap bases, glycerin blocks and melt and pour bases may not involve a chemical reaction because the saponification reaction has already occurred.

Soap-free cleansers, such as syndet bars, are generally made by mixing the ingredients, without a chemical reaction.

You should do your own research to understand whether a chemical reaction has occurred in your soap-making process.