Add Purchase Order Lines to an existing PO but no new PO creation without Purchase Requisition

Summary: Currently there is a requirement to configure the system so that Purchase Orders cannot be created without an associated Purchase Requisition. This is currently achieved by creating a custom Buyer role and removing the "Create Purchase Order" privilege. However, there is also a business need to allow users with this custom Buyer role to add new PO lines when processing a change order. In the current setup, adding new PO lines during a change order is not permitted unless the "Create Purchase Order" privilege is granted, which would also enable direct PO creation.

Is there any setup change or workaround available to achieve this requirement.