“County peace officer” shall also include persons employed by a county parks and recreation department whose primary responsibility is maintaining the peace and whose duties include law enforcement, emergency medical care first response, or fire suppression and prevention in the Park Ranger class series.

This section shall not apply to the employees of any contracting agency nor to any agency unless and until the contracting agency elects to be subject to the provisions of this section by amendment to its contract with

the board, made as provided in Section 20474 or by express provision in its contract with the board.