Tex. Local Government Code § 158.038

(a) A person who is an employee of a department on the date that a civil service system is adopted under this subchapter in the department may not be required to take a competitive examination or perform any other act under this subchapter to maintain the person's employment.

(b) The sheriff of a county with a population of 3.3 million or less may designate as exempt from the civil service system:

(1) the position of chief deputy;

(2) four positions of major deputy;

(3) one or more positions in the office of departmental legal counsel; and

(4) additional positions in the department; provided, however, that the sheriff may not designate as exempt a total of more than 10 positions.

(c) The sheriff of a county with a population of more than 3.3 million may designate as exempt from the civil service system:

(1) the position of chief deputy;

(2) one or more positions in the office of departmental legal counsel; and

(3) additional positions in the department, not to exceed 25 in number, that have been determined by the civil service commission to be administrative or supervisory positions; provided, however, that the sheriff may not designate as exempt any position in the deputy classifications of captain or below. The designation of any such additional exempt position by the sheriff shall not diminish the number of positions within the deputy classifications of captain or below.

(d) At the time a new sheriff takes office, an employee holding an exempt position may be transferred to the nonexempt position held by the employee immediately before being promoted to an exempt position. A person who was not an officer in the department when appointed to an exempt position may be transferred only to an entry level position in accordance with the system's civil service rules.