Retrospective amendment of CENVAT credit rule validates past credit actions, bars suits and mandates recovery. Section 83 retrospectively amends Rule 6 of the CENVAT Credit Rules, 2001 as per the Fifth Schedule, validating actions taken under the amended rule during the transitional period as if the amendment had been in force at all material times, prohibiting suits or enforcement against the Central Government or Central Excise Officers in respect of recoveries under the amendment, directing recovery of unpaid amounts within a prescribed period after enactment, and deeming the Central Government to have had retrospective rulemaking power; it also removes criminal liability for acts not punishable absent this section.