This is another often asked question so I'm adding it as a sticky.

A child can NEVER make the choice.

In no US state can a minor child (under 18) make the decision as to which parent to live with. Only a judge can make that decision. Some areas have guidelines on how much weight to put on a child's preference based on their age, but the decision is still up to the judge based on the best interests of the child.

If the NCP wants to modify a custody order, they have to file with the court for a modification. The court will review the case and make a decision.