(a) A person who is a retired or former judge shall, before accepting an assignment as a visiting judge of a statutory county court, take the oath of office required by the constitution and file the oath with the regional presiding judge.
(b) A regional presiding judge shall maintain a file containing the oaths of office filed with the judge under Subsection (a).
(c) A retired or former judge may be assigned as a visiting judge of a statutory county court only if the judge has filed with the regional presiding judge an oath of office as required by this section.