The contract may include any provisions consistent with this part and necessary in the administration of this system as it affects the public agency and its employees.

Whenever in this part an election is given to contracting agencies to subject themselves and their employees to provisions of this part otherwise not applicable to contracting agencies and their employees by amendment to their contracts with the board, any contract made after the effective date of the provision giving the election may include any provisions necessary to give effect to the election of the contracting agency.