Probably not. If you did a final order 9 months when your son came to live with you, the modification can only go back to the date they file to change it. If you and your ex did a temporary order the court may be able to go back to when your son came to live with you. I would set the money aside just in case. You can voluntarily increase your withholding but the State Disbursement Unit will probably mess it up so you are better off .
Another option is for you and your ex to make an appoint with the Attorney General's office, go in together and get an agreed modification done. If she has a lawyer and you don't, you can also go see the lawyer and get it fixed. Good luck.
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