Except as it may be further limited by this part, a constitution and bylaws, amendments thereto, or charter and charter amendments shall be considered adopted, ratified, or revoked if a majority of those actually voting are in favor of adoption, ratification, or revocation. The total vote cast, however, must be at least 30 percent of those entitled to vote, unless, with regard to amendments, the constitution provides otherwise. The names of persons appearing on the registration list who have not reached eighteen years of age by the date of the election, shall be removed from the list of registered voters when determining whether the required percentage of participation has been achieved. Unless the existing constitution or charter provides otherwise, none of the actions cited in this section shall become effective until they are approved by the Secretary. The validity of any charter ratification shall be dependent upon the tribe first having reorganized. Duly ratified charters shall be revoked or surrendered only by Act of Congress.