Notwithstanding the provisions of any general or special act or compact adopted by referenda to establish a regional school district, the provisions of this part shall apply to the regional school districts in existence on June 24, 1969, except as provided below.

(a) Nothing in this part shall be construed to require an existing regional school district to change the composition of the membership of its board of education or their terms of office or as prohibiting the selection of members of such boards by appointment.

(b) If the board consists of nine members, three from each member town, such members may be elected on a rotating basis each year for terms of three years. If any adjustments are necessary to achieve this system, the regional school district shall use the procedures provided in § 10-47c to make the necessary changes, provided the term of office of no incumbent shall be shortened.

(c) Any such school district may change the representation of the member towns on the regional board or change the term of office of such members to four years in accordance with the procedures provided in § 10-47c. If the latter change is made, the member towns may elect their representatives on the regional board of education in accordance with subsection (b) or (c) of § 10-46 as determined by the legislative body of each town.