Any member of or subscriber to a rating organization to whom the provisions of Article 5 of this chapter are applicable may make written application to the department for permission to file a uniform percentage decrease or increase to be applied to the premiums produced by the rating system so filed for a kind of insurance or for a class of insurance which is found by the director or his designee to be a proper rating unit for the application of such uniform percentage decrease or increase or for a subdivision of a kind of insurance (a) comprised of a group of manual classifications which is treated as a separate unit for rate-making purposes or (b) for which separate expense provisions are included in the filings of the rating organization. The application shall specify the basis for the modification and must be accompanied by the data upon which the applicant relies. A copy of the application and data must be sent simultaneously to the rating organization.