In 2007 I through mediation agreed to a shared parenting agreement after being sole custodial parent for ten years due to medical reasons. Well in judgment decree it says that father is now primary custodial and residential and I am just custodial and non-residential father has used this to pursue child support against me and taken my social security benefit from me thAT I RECEIVE FOR MY SON. He was needless to say underhanded in his dealings... I go back to court next month to have the agreement changed to say[I] both parents are custodial and residential when child is with them... what are the chances of judge agreeing to these new terms

What state are you in? And I don't see a judge agreeing to your terms. Was the social security for the child that you no longer have custody of or a different child?

If you were receiving SS benefits for a child that you are no longer the primary custodian of, then it makes sense that it goes to the primary custodian.

As to your chances of getting equal custodian status, that is rare. Does the father live within the same school district? How old is the child?

What is the breakdown on your shared parenting agreement ? When are the children with you and with him ?