Back up a second. I'll re-post one of my prior comments:
So it is NOT just a Notarized Document. It is a document sent to the Court to modify your legal agreement. That changes things.
That seems to be a legal document for 'other' legal purposes (divorce/family court). That means two things:
(1) That probably does NOT allow your husband to claim the child for TAX purposes (it doesn't seem to fit the requirements to replace Form 8332). Strictly for tax purposes, you would get to claim him every year.
(2) However, it also gives your Ex full right to bring you to 'family' court and the Judge would demand that you give the Ex Form 8332 (assuming you don't negotiate a change these legal documents). So it seems to be a legal document that REQUIRES you to give your Husband Form 8332, which allows him to claim the child.
So (1) you hypothetically don't need to revoke 8332, because that document shouldn't allow him to claim your son, and (2) If you do fully claim your son (the exemption and Child Tax Credit), it appears you will be violating Court documents, and your ex can ask a Judge to MAKE you sign Form 8332.