California Code, Revenue and Taxation Code - RTC § 678

The board may issue an interim certificate to a current assessor or to any person who is currently employed by the office of the county assessor, and who is making change in ownership or exemption decisions in order to afford that person the opportunity to apply for and take an examination, the successful passage of which would qualify the person for a certificate pursuant to this article. The board shall not issue an interim certificate for a duration that exceeds four years, unless the person has been duly elected or appointed to the office of assessor. The board shall not renew an interim certificate.