Whenever, in any law or treaty or in any patent issued to Indian allottees for lands in severalty pursuant to such law or treaty, there appears a provision to the effect that the lands so allotted cannot be alienated without the consent of the President of the United States, the Secretary of the Interior shall have full power and authority to consent to or approve of the alienation of such allotments, in whole or in part, in his discretion, by deed, will, lease, or any other form of conveyance, and such consent or approval by the Secretary of the Interior on and after September 21, 1922, had in all such cases shall have the same force and legal effect as though the consent or approval of the President had previously been obtained: Provided, however, That the approval by the Secretary of the Interior of wills by Indian allottees or their heirs involving lands held under such patents shall not operate to remove the restrictions against alienation unless such order of approval by said Secretary shall specifically so direct.