Hi,
Your requirement differs then .....
Initially you wanted service Tax on Unplanned delivery cost needed load on the Material cost and now wanted---service tax on Unplanned delivery that to be treated as Setoff condition.
1st decide your requirement------ Service Tax on Unplanned delivery cost will be treated by adding service tax cost to inventory account (non-deductable) or treated as Setoff ( deductable)
For your 2nd requirement- keep service tax code for Setoff ( deductable) in your purchase order and
do "Invoice" in MIRO t.code to post "Unplanned Delivery Cost" by entering Service Tax Code which has Setoff ( deductable) conditions.
Regards,
Biju K