If at or about the time of submitting such amendment, Congress, either in the resolution submitting the amendment or by statute, prescribes the manner in which the conventions shall be constituted, and does not except from the provisions of the statute or resolution the states which theretofore have provided for constituting such conventions, this article shall be inoperative. The convention shall in such event be constituted and shall operate as the resolution or act of Congress directs, and all officers of the state who are by the resolution or statute authorized or directed to take any action to constitute a convention for this state are authorized and directed to act thereunder and in obedience thereto with the same force and effect as if acting under a statute of this state.