Either parent may file a petition to modify a child custody order—but usually only when there is a substantial change in circumstances that affects the child (including changes in one or both of the parents’ lives) that justifies the court revisiting and possibly modifying the earlier child custody order.

The petition to modify child custody generally must be filed in the same court in which the parents’ divorce case was decided. But if the child lives in a different county or state, the courts of the county or state where the child lives may be the proper place to file a petition to modify a child custody order.

In New Mexico, either parent has the right to file a petition to modify a child custody order if there is a substantial change in circumstances that affects the welfare of the child. This could include significant changes in the life of either parent or the child. The standard for what constitutes a substantial change is generally high, as courts prioritize stability in a child's life. The petition to modify custody must typically be filed in the court that issued the original custody order. However, if the child has since moved to a different county or state, the petition may need to be filed in the jurisdiction where the child currently resides. This is in line with the Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA), which New Mexico has adopted, and which dictates that child custody matters should be handled in the child's home state, defined as where the child has lived for the six months immediately preceding the filing of the petition, unless there is an emergency situation. It is important for parents to consult with an attorney to understand the specific legal requirements and to ensure that the petition is filed in the appropriate venue.