Retrospective amendment power enables refunds and bars prosecution for acts not punishable absent amendment under excise law Provision deems a specified notification under the Central Excise Act to be amended retrospectively for listed tariff items and chapters, confirms the Central Government's retrospective amendment power at all material times, mandates refund of excise duty collected but not due if the notification had been in force, conditions refunds on existing statutory provisions and a prescribed limitation for claims, and bars punishment for acts that would not have been punishable but for the retrospective amendment.