Neither the repeal of former Chapter 2 of this part, the reenactment of this chapter nor the amendment of any provision of this chapter shall have the effect of terminating or invalidating any stabilization and marketing plan, including provisions thereunder regarding minimum prices to be paid producers for market milk, established by the director pursuant to this chapter or former Chapter 2 prior to the effective date of the repeal, enactment, or amendment. The director shall, however, establish minimum prices pursuant to the provisions of the enactment, or amendment at the earliest practicable date after the effective date of the amendment.