(1) In the case of casualty and surety insurance to which this article applies any such insurer may make written application to the commissioner 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 commissioner 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. Such application shall specify the basis for the modification and shall be accompanied by the data upon which the applicant relies. A copy of the application and data shall be sent simultaneously to such rating organization; and
(2) In the case of fire and marine insurance to which this article applies any such insurer may make written application to the commissioner for permission to file a deviation from the class rates, schedules, rating plans or rules respecting any kind of insurance, or class of risk within a kind of insurance or combination thereof. Such application shall specify the basis for the modification and a copy thereof shall also be sent simultaneously to such rating organization. In considering the application for permission to file such deviation the commissioner shall give consideration to the available statistics and the applicable principles for rate making as provided in section three of this article.
(b) The commissioner shall, after notice to such insurer and rating organization, and hearing, unless hearing is waived by such insurer and rating organization, issue an order permitting the modification for such insurer to be filed if he finds it to be justified and it shall thereupon become effective or issue an order denying such application if he finds that the modification is not justified or that the resulting premiums would be excessive, inadequate or unfairly discriminatory. Each deviation permitted to be filed shall be effective for a period of one year from the date of such permission unless terminated sooner with the approval of the commissioner.