A custody modification that is agreed between the parties. A custody modification is fairly involved because it changes custody and child support. Make sure that I receive the statutorily required 6 months paystubs and 2 years tax returns from both parties. I have a form for you to complete to see if you are eligible for any deductions. You pay the filing fee. You file it with the court. You are the one who follows procedures to finalize the child support modification.