(1) For any calendar year after its first two full calendar years of operation, no domestic mutual insurer on the cash premium plan, other than one issuing nonassessable policies, shall incur any costs or expense in the writing or administration of property, disability, and casualty insurances (other than boiler and machinery or elevator) transacted by it which, exclusive of losses paid, loss adjustment expenses, investment expenses, dividends, and taxes exceeds the sum of

(a) forty percent of the net premium income during that year after deducting therefrom net earned reinsurance premiums for such year, plus

(b) all of the reinsurance commissions received on reinsurance ceded by it.

(2) The bylaws of every domestic mutual property insurer on the assessment premium plan shall impose a reasonable limitation upon its expenses.