(a) A person who on August 30, 1971, was an employee of an eligible county under this subchapter may not be required to take a competitive examination or perform any other act to maintain the position held on that date.
(b) This subchapter does not apply to:
(1) assistant district attorneys, investigators, or other employees of a district or criminal district attorney, except as provided by Section 158.007;
(2) the official shorthand reporter of a court; or
(3) an elected or appointed officer under the constitution.