Retrospective classification of oil refining as manufacture validates past excise levies and bars refund claims for the period. The amendment retrospectively treats specified refining processes of edible vegetable oils as manufacture for 1 March 1986-28 February 2005, validates excise duties levied during that period as if the classification had always applied, bars proceedings for refund or enforcement of refunds relating to those duties, and declares the Central Government had retrospective power to effect the amendment while ensuring no new criminal liability arises solely from this provision.