In any town not divided into voting districts, the place of holding elections may be determined by the legislative body of such town. In towns divided into voting districts the place of holding elections shall be determined as provided in § 9-169 or any special act, whichever applies. Except as provided in § 9-169a, state elections shall be held at the usual place or places of holding elections in the town or the voting districts thereof, as the case may be, unless the registrars of voters, in writing, have designated to the clerk of such town, at least thirty-one days before any such state election, a different place or places for holding such election. Unless otherwise provided by special act, the place of holding city or borough elections shall be determined by the legislative body of such city or borough. Any provision of any charter or special act to the contrary notwithstanding, the place or places of holding an election shall be determined at least thirty-one days prior to such election, and such place or places shall not be changed within the period of thirty-one days prior to such election except that, if the municipal clerk and registrars of voters of a municipality unanimously find that any such polling place within such municipality has been rendered unusable within such period, they shall forthwith designate another polling place to be used in place of the one so rendered unusable and shall give adequate notice that such polling place has been so changed.