Section 16A. In every city except Cambridge and every town which accepts this section in the manner hereinafter provided, there shall be a board of election commissioners, hereinafter called the board, which, except as otherwise provided, shall have all the powers, rights, duties and liabilities of boards of registrars of voters, and, with respect to elections, of city and town clerks, either under general or special law, and which shall be the lawful successor of said registrars, and, with respect to elections, said clerk. Immediately upon such acceptance, the said registrars of voters and, in so far as they relate to, or are required for use in, the conduct of elections, the said clerk shall deliver to the board all books, papers, records and all other property in their possession. The board shall consist of four persons, of whom two shall always represent each one of the two leading political parties, as defined in section one of chapter fifty. They shall receive such compensation as the city manager, or mayor, and city council, or the town, may determine. The members of the board of registrars of voters in office at the time of such acceptance shall be members of said board of election commissioners, and shall serve until the expiration of their respective terms and until their successors are appointed and qualified; provided, that, if the city or town clerk is then a member of said board of registrars, the mayor, subject to approval by the board of aldermen, the city manager, or the selectmen shall appoint one member of said board of election commissioners for a term of four years beginning April first next following. As the terms of the several election commissioners expire, and in case a vacancy occurs in said board, the mayor, subject to approval by the board of aldermen, the city manager or the selectmen, shall so appoint their successors that the members of the board shall equally represent the two leading political parties as defined as aforesaid. In a town which accepts this section, every such appointment shall be made from a list to be submitted by the town committee of the political party from the members of which the position is to be filled, containing the names of three enrolled members of such party resident in the town, selected by a majority vote at a duly called meeting, at which a quorum is present, of such committee; and every member of said board shall serve until the expiration of his term and until his successor has qualified; provided, however, if the chairman of the town committee has not submitted such list to the selectmen or the appointing authority within forty-five days after a notification to said chairman by certified mail, the selectmen or the appointing authority shall make said appointment without reference to such a list. Such appointments shall be for terms of four years beginning April first, except that any appointment to fill a vacancy shall be for the unexpired term. The board shall organize annually in the month of April by the choice of a chairman and a secretary. In case the members are unable to agree upon a chairman and a secretary, such officers shall be designated by the mayor, the city manager or the selectmen, as the case may be. The secretary shall keep a full and accurate record of the proceedings of the board and shall perform such other duties as the board may require. All the powers, rights, privileges, liabilities and duties relating to caucuses, primaries and elections by law vested in and imposed upon mayors, city managers, boards of aldermen, selectmen, city or town clerks and board of registrars of voters, except the power and duty of giving notice of elections and fixing the days and hours of holding the same, shall be vested in and performed by the board of election commissioners. The board may appoint such assistant commissioners and such assistants as it deems necessary, who shall at all times equally represent the two leading political parties as defined as aforesaid. Said assistant commissioners shall have such powers and perform such duties as are prescribed by this chapter for assistant registrars of voters, and shall perform such other duties as the board may require. Except in Boston, persons appointed to serve temporarily as assistant commissioners, or as temporary assistant commissioners, shall not be subject to chapter thirty-one. This section shall become effective in a city having a Plan E charter by the affirmative vote of a majority of all the members of the city council, and, in the case of other cities, by vote of the city council, subject to the provisions of the charter, and in a town by a majority vote at an annual town meeting.