Any farm mutual insurance company may amend its articles of incorporation to include other adjoining counties, provided that the company’s net written premium did not exceed 3 times its policyholders’ surplus as reported in its last financial statement. Subject to the approval of the Director of Insurance, any company having $150,000 policyholders’ surplus may add one contiguous county to its territory, and may add one additional contiguous county for each additional $50,000 policyholders’ surplus thereafter.