Incoterms in PO not editable

Hi,

The requirement is not to allow changing the Incoterms in PO thro' change/release T. codes. only when creating PO thro' ME21N, this field can be editable.

Hence, I have configured thro' OLME-Purchase Order-Define screen layout at document level as detailed below.

AKTH/ME21/ME21N/NBF/PT0F - Incoterms part 1 and Incoterms part 2 as "opt. entry"

AKTV/ME22 - Incoterms part 1 and Incoterms part 2 as "Display"

But, in ME21N, the Incoterms at the PO header level is in display mode and so not editable.

Please guide me on how to proceed.

Thanks.

Regards,

Siva