Hi,
Change of the document could be done either in Enjoy transaction, FB02 or via report, e.g. FBL3N. You should include all those in the check. But, from other hand, why would you need a pre-requisite of transaction code at all? Just keep it blank and the check would happen in all cases. If it has to be only for vendor lines, then set a condition of BSEG-KOART = 'K' and for relevant document types (BKPF-BLART).
Regards,
Eli