Your FI / Legal departments would be able to tell you the accessible value on which excise has to be calculated. There would not be any impact in the excise part as you will enter the price any ways in the Purchase order which is a Base for Excise duty calculation.
Accessible value is required in J1ID only in case if you want to Create Outgoing excise invoices (For STO with MM route / Excise invoice for Return PO / Excise invoice for any other purposes say OTHR transaction type) or if you want to reverse the Credit in Subcontracting process.