Does marriage nullify a former custody agreement?

South Carolina, unwed parents created a joint custody and visitation agreement. They later married. Husband is in the Army, and the parents and child lived as a family in Hawaii for 18 months, his current duty station. Wife left 3 months ago, and brought the child back to SC. Wife left child with paternal grandmother, visiting a few hours per week, but not providing support. She asked father to take the child for 6 months, but after they agreed, she wanted things in writing, such as, she pays no support, he sends child back in 6 months (though she is admittedly doing cocsine), and many other new conditions. Father flew child to Hawaii, without mother's knowledge until they had arrived in Hawaii. Now mother is saying that the Pre-marriage custody agreement requires a 48 hour notice, and that father is now in contempt of court. They have not yet filed for divorce, nor legal separation. Does the former custody agreement stay in effect even during marriage?