Unable to add item from requisition (RSSP)

Summary:

Unable to add item from requisition which has been approved and purchase order has been created (RSSP)

a) Purchase Order created using requisition using RSSP.

b) Would like to add a new line at the requisition level not at the Purchase Order (Change Order).

c) Since the client does not want to give the PO related roles to the employees.
(ANCILLARY QUESTION: Why is there no shop option like it is available in classic SSP)

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):