Even where the circumstances of a case have significantly changed, a court will only modify a custody order if it is in the best interests of the child. (info.legalzoom.com)
The court will not modify a custody arrangement if there has only been a minor change in circumstances. (info.legalzoom.com)
In some cases, the court will also look at the child's preferences when deciding whether to modify the custody agreement. (info.legalzoom.com)