How can we restrict the selection of purchasing categories in RSSP?

Summary:

We need to restrict the selection list of purchasing categories for non-catalog requests in RSSP.
Using SmartForms does not meet our needs, as we also allow users to access the "Enter Requisition Line" option to give them the flexibility to create PRs using generic items.
However, these generic items are linked to purchasing categories that should not be used for non-catalog requests.

In addition, we would like certain purchasing categories to be restricted depending on the Procurement/Requisitioning Business Unit, as there is no mapping set for some categories from one country to another.

Thank you for your feedback