You can post an adjustment entry for Excise amount in J1IH using Additional Excise option. Please note that J1IH doesnot propose the difference amount in MIRO transaction. MIRO transaction fetches the Excise duties whatever posted during J1IEX for that Excise invoice from J_1IGRXREF table.
If you want to post the difference Excise amount, use GL account tab in MIRO and adjust it. Else use FB60 and post the difference to the Vendor.