(a) The Commission may establish a merit system that includes all of its employees except:
(1) the general manager, secretary, treasurer, and chief engineer;
(2) the head of a department;
(3) (i) the inspector general; and
(ii) any temporary employee of the Office of the Inspector General appointed under § 17-603 of this article; and
(4) a part time, temporary, or contract employee.
(b) The Commission may:
(1) appoint or promote a merit system employee to the position of general manager, department head, or inspector general or designate a merit system employee as the general manager, department head, or inspector general on an acting basis;
(2) retain the employee in the merit system in the position or grade from which the employee was appointed or promoted; and
(3) continue to exclude the positions of general manager, department head, and inspector general from the merit system.