Customs exemption amendment delays applicability for specified goods and sets a per unit ceiling with ad valorem comparison for duty assessment. Amendment inserts a new serial entry 491D postponing exemption applicability until the prescribed future date, adds a Table entry fixing a per kilogram duty rate for all goods under the tariff heading, and introduces a condition that if the duty per kilogram calculated at the stated ad valorem percentage exceeds the fixed per kilogram rate, the ad valorem derived amount shall apply for assessment.