The provisions of this act shall not apply to or affect any valid rental agreement entered into prior to the effective date of this act, nor shall it apply to or affect any conduct or transaction of the parties to such rental agreement, if such conduct or transaction is in accordance with and pursuant to such rental agreement; but the provisions of this act shall apply to and govern any renewal, extension or modification of any such rental agreement, where such renewal, extension or modification is effected on or after the effective date of this act.