(a) A judge or clerk of the supreme court, the court of criminal appeals, a court of appeals, or a district court, or a sheriff may not appear and plead as an attorney at law in any court of record in this state.
(b) A county judge or county clerk who is licensed to practice law may not appear and practice as an attorney at law in any county or justice court except in cases over which the court in which the judge or clerk serves has neither original nor appellate jurisdiction.
(c) A county clerk who is licensed to practice law may not appear and practice as an attorney at law in the supreme court, the court of criminal appeals, a court of appeals, or a district court unless the court in which the clerk serves has neither original nor appellate jurisdiction.