(a) Enforcement.--A party to an agreement regarding matters within the jurisdiction of the court under this part, whether or not the agreement has been merged or incorporated into the decree, may utilize a remedy or sanction set forth in this part to enforce the agreement to the same extent as though the agreement had been an order of the court except as provided to the contrary in the agreement.

(b) Certain provisions subject to modification.--A provision of an agreement regarding child support, visitation or custody shall be subject to modification by the court upon a showing of changed circumstances.

(c) Certain provisions not subject to modification.--In the absence of a specific provision to the contrary appearing in the agreement, a provision regarding the disposition of existing property rights and interests between the parties, alimony, alimony pendente lite, counsel fees or expenses shall not be subject to modification by the court.