The answer is yes it can upon a change in either parties income of 10% up or down. If a substantial amount of time has passed a review can be requested to see if a modification is warranted.
A person paying child support cannot make an agreement with the person receiving child support to pay an amount less than what was ordered by the court. Any changes or modifications must be done through the court or they will not be valid and the person paying support will be responsible for any arrearages that came out of the original order.
A modification requires a new court filing fee and an attorney to represent you. Current income figures from both parties must be supplied as well as insurance costs or daycare cost related to the minor children. All this information will be applied to the child support guidelines and a new amount calculated and approved by the court.