There shall be no part-time district attorneys or part-time legal assistants to district attorneys; however, any person not serving as a legal assistant to the district attorney who is appointed by the Governor to serve as district attorney to fill a vacancy occurring in such office until such office shall be filled by a special or regular election as provided by Sections 23-15-193, 23-15-833 and 23-15-843 shall be allowed to engage in the private practice of law while holding the office of district attorney pursuant to such appointment.