(a) Rates may be modified to produce premiums for individual risks in accordance with filed rating plans which establish standards for measuring variations in hazards or expense provisions. Those standards may measure differences among risks that can be demonstrated to have a probable effect upon losses or expenses. The modification shall apply to all risks under the same or substantially the same circumstances or conditions.
(b) This provision does not apply to filed modification plans which may be offered to an insured including, but not limited to, retrospective rating plans and composite rating plans.