How to default OI Routing Instructions Text in me21n , even before saving the PO

Hi ,

When creating a PO through me21n , in the texts tab ..

OI Routing instructions  needs to have a default text even before the PO is
saved. Is this thing possible . I found one exit

EXIT_SAPMM06E_022

where I tried changing , but where can I pass the text in thead structure ?

Thanks

Barun

Accenture