For good cause, before the expiration of the period allowed for appeal after the order of final distribution of the administration of the estate of a decedent or ward, the court may vacate or modify its orders, judgments and decrees, or grant a rehearing therein, except that no such power shall exist as to any orders, judgments or decrees from which an appeal has been taken, prior to a final disposition thereof on such appeal, or to set aside the probate of a will after the time allowed for contest thereof. No vacation or modification under this section affects any act done or any right acquired in reliance on any such order, judgment or decree.