How to restrict the Qty & Val in MIRO for Customs

Hi Xperts

I have a reqmnt.

I have found in case of Import procurement process , we are not using GR based IV Indicator in the PO.Also we need to perform MIRO for Customs prior to GR.

1. Hence users need to manually enter the qty/val for all the duties during MIRO(Custom). I have also chkd that users can enter more than the PO-Qty & more then PO-Condition Value as well during that.

2. Also user can do MIRO(for Custom) multiple times as they wish, though MIRO(Custom) has already been completed for that item.

Ho to restrict the above in AP?Plz suggest.

Rgds

Soumick