Retrospective amendment power validates past excise notifications and bars challenges while enabling recovery with interest. The provision retrospectively amends two Central Government notifications under section 5A of the Central Excise Act, deems actions taken under those notifications to have been valid as if the amendments had been in force at all material times, and deems the Government to have had retrospective amendment power. It bars any suits or enforcement challenging such actions, requires recovery of duties, interest or other charges within a statutory short period with interest thereafter on unpaid sums, and declares that no act or omission shall be punishable if it would not have been an offence but for the retrospective amendment.