how is child support determined and calculated

Child support formula: When my divorce judgment was entered I agreed to a parenting time arrangement that gave me less than 50% of overnights with my children. A few years after the divorce was final the state changed the child support formula was changed to pay the parent with >50% of the overnights more child support. My question is, since the orignal agreement was made with a certain set of assumptions:

1. Can I win a fight over changing to the new formula for child support (i.e., achieve a grandfather clause on this forumla)?

2. If (1) is no, can I use this change in law as a legitimate "change in circumstances" to argue for more overnights with my children? - Is this your question? Add additional information