When custody must be spelled out because of a couple's divorce, the custody arrangement usually becomes part of the divorce decree. The decree names the parent with whom the child will live, how visitation will be handled, and who will provide financial support. Courts consider a custody award to be subject to change until the child comes of age, and in most states proof of a "change in circumstances" may overturn an earlier award. This flexibility is intended to allow for the correction of poor or outdated decisions, but it consequentially enables some parents to wage bitter custody battles that can last for years.

http://www.alachuaclerk.org/forms/MotiontoRevokeTCustody.pdf

legal terminology used for revoking/dropping rights

Ineligible: legally disqualified to function as a juror, voter, witness, etc, or to become the recipient of a privilege.