This is NOT advisable for several reasons.
First, the ordering containing a child support obligation could ostensibly be in effect for many years, depending on the age of the child when it is first submitted to the court. Second, costs of living increase, people have more children, jobs are lost, two incomes become one; there are a variety of events that could cause a party to regret agreeing to pay a higher amount of child support than guideline amount. Third, there are penalties associated with failure to pay child support obligations; a person does not want to set themselves up for criminal or punitive sanctions for failure to pay if they could have avoided it by paying the guideline amount.
If a party insists on providing more for their child than the guideline amount it would be advisable to do it informally. A party can purchase school supplies, clothing and toys, pay for ballet lessons or put the money in a college fund rather than committing to a higher amount of child support in a court order. While it is admirable that a parent may want to go above and beyond the minimum support obligation, it shouldn’t be at their expense should circumstances change and they are unable to pay the increased support obligation.