Hi Mick,
A property settlement is different from a custody arrangement. If you want to vary the property settlement, this will depend on how it is made. If it was made personally with no court involvement, then you simply need to agree to another one with your ex. If there was court involvement and the settlement is in the form of an order (financial order or consent order), you will need to apply to court to vary the order. The fact that you have the children full time, meaning need for more child maintenance, will help your case. I doubt that you will get the allocations reversed, however, you may be able to ask for a bit more from the other parent in child maintenance and support. The court will again, look at the relative positions of the two parents (income, expenses and liabilities), and ask what is fair and just in the situation.