Value addition based excise exemption: duty measured on value addition with CENVAT-first payment and refund procedures. Notification shifts exemption basis for goods in Sikkim to duty on value addition, prescribing percentage rates by tariff chapter, capping payable duty at duty actually paid excluding CENVAT, requiring manufacturers to exhaust CENVAT credit before cash payment, and establishing monthly reporting, refund or account current credit options, compliance verification, recovery for irregular credits, and a mechanism for fixation of a Commissioner determined special rate based on prior year financials with provisional refunds and government oversight.