Negotiating away child support is not supported by law, thus statute would override any agreement you make in your decree. It would be like getting your ex to agree to 50 lashes anytime she is late bringing the child to you. A judge can sign off on it, but it's unenforceable. Neither is within the scope of the law.
In most states, she could call CSE the day you sign the degree (after you've given away tens or hundreds of thousands of assets in lieu of child support) and your support would start that day.
“There are those that look at things the way they are, and ask why? I dream of things that never were, and ask why not?”