(a) Any mass merchandising agreement may provide for the readjustment of the rate of premium based on experience at the end of the first year for any subsequent year of insurance, and such readjustment may be made retroactive only for the policy year.
(b) If a policy dividend is declared or a reduction in rate is made or continued under any mass merchandising plan, the excess, if any, of the aggregate dividends or rate reductions under the policy and all other group insurance policies of the policyholder over aggregate expenditure for insurance under such policies made from funds contributed by the policyholder, or by an employer of an insured person, or by a union or association to which an insured person belongs, including expenditures made in connection with administration of such policies, shall be applied by the policyholder for the sole benefit of insured employees.