The district attorney of any prosecutorial unit having a population of less than 100,000 may appoint one or more assistant district attorneys as necessary to carry out the duties of his or her office and as may be requested by the department of administration authorized in accordance with s. 16.505. Any such assistant district attorney must be an attorney admitted to practice law in this state and, except as provided in s. 978.043(1), may perform any duty required by law to be performed by the district attorney.