These are typically limited to cases where the modification is necessary for the safety of the child.
Most states do not allow for modifications to be made to a child custody agreement without the consent of both parties. Some states do allow for certain types of modifications, however. These are typically limited to cases where the modification is necessary for the safety of the child.
If you and your ex-spouse are unable to agree on a modification to your child custody arrangement, you may have to go through the court system in order to get a judge to approve the change. This can be a long and costly process, so it is always best to try and work out an agreement with your ex-spouse first.