There is nothing to stop you just dividing things up. This can be formalised as a separation agreement if you wish. You can limit the application of the new law by ordering your affairs - for example by making a will or appointing a guardian. Sometimes it steps in when it is unclear what should happen - for example when people can't agree or if you die without a will. Where all of this is decided in advance, it's not so likely to be needed.
Casual partners have no rights to property.
It basically looks at the contributions that each person has made. If your relationship ended before 28 June 1999, the changes won't apply. No, social security isn't affected. Social security is governed by the Federal Parliament. This Act only deals with NSW laws.