(1) Subject to Subsection (2), an optional plan, after going into effect following an election held under Section 17-62-501, may be amended by an affirmative vote of two-thirds of the county legislative body.
(2) Notwithstanding Subsection (1), an amendment to an optional plan that is in effect may not take effect until a majority of registered voters voting in a general or special election at which the amendment is proposed approve the amendment, if the amendment changes:
(a) the size or makeup of the legislative body, except for adjustments necessary due to decennial reapportionment; or
(b) the distribution of powers between the executive and legislative branches of county government.