Retrospective amendment power authorises revision of notified interest rate under section 50, effective from the notification's commencement. Clause 118 amends notification G.S.R. 698(E) to substitute the notified interest rate under sub-section (3) of section 50 of the Central Goods and Services Tax Act and declares that substitution to operate retrospectively from the specified effective date; it also deems that the Central Government had and has the power to effect such retrospective amendment of the notification.