Section 20. Towns divided into voting precincts may, for their annual town election, establish precinct voting for all town officers to be chosen thereat, by accepting this section at a meeting held seventy days at least before the annual town meeting. The acceptance of this section or corresponding provisions of earlier laws may be revoked by the town at a meeting held seventy days at least before the annual town meeting; and if so revoked this section shall cease to be in force therein. Towns by vote or by-law may authorize voting precincts at special elections of town officers.