Customs tariff amendment substitutes a higher ad valorem rate and omits a prior paragraph, changing the duty structure. Under powers of sub-section (1) of Section 25 of the Customs Act, 1962, the amendment substitutes the ad valorem component in the opening paragraph of Notification No. 275/87 Cus with a higher ad valorem rate while retaining the stated per tonne charge, and omits paragraph 2 of the original notification.