The court is unlikely to go back and modify support before the action is filed and the person is served. You can try to seek to modify the amount of arrears taken from you.
An appeal to the court to reduce the support can be done if income has declined or there is an argument to make about extenuating circumstances that you feel the court did not take into consideration. These may include custody of another child or financial hardships; if you have another child to support, the law allows for asking to reduce child support. If you had become unemployed since the amount of his payments were calculated, the judge may say you can reduce support.
Check with your own attorney to make sure your children's position is best represented.
Note: This post is for education only and does not create an attorney client relationship between the questioner and the out-of-state attorney. This website is not a substitute for legal advise by an attorney in your state. Seek one to confirm or check the observations made by the out-of-state attorney. The law changes and is different from jurisdiction to jurisdiction.