Limit PO lines creation from requisition/ other system

Hi,

Our business would like to request to limit the PO lines creation from requisition/other system (example: 10 lines per PO only). As I have searched in the community, there are suggestion on forms personalization. But we are using Standard Purchase Import program when creating the PO. Is it possible to create a new process in CREATEPO workflow wherein after insert of record in PO interface tables, we will cut/limit the creation of lines so that when the spawned import program will create the PO based on the limited lines (which was added in the new wf process).

I would also like to ask for your assistance on inserting records in PO interface tables so we can create manually and observe how these records were created as PO.