(a) Best interest of the child.–Upon petition, a court may modify a custody order to serve the best interest of the child.
(b) Applicability.–Except as provided in 51 Pa.C.S. § 4109 (relating to child custody proceedings during military deployment), this section shall apply to any custody order entered by a court of this Commonwealth or any other state subject to the jurisdictional requirements set forth in Chapter 54 (relating to uniform child custody jurisdiction and enforcement).