Restricting Items during Purchase Requisition creation

Dear Experts,

I want to restrict the creation of Purchase Requisition in 2 different scenarios. Any pointers on how to achieve this would be of great help.

Scenario 1:

At the Item level in PIM module, Min-Max planning is enabled for around 1500 Items (approximately). As you know, Min-Max planning creates a PR automatically when the minimum quantity (on-hand) is reached. Since these Items have Min-Max planning enabled, we should restrict ALL the users from creating a PR directly in the system. If we cannot put any restrict PR creation, is there a way we can auto-reject such PRs that are directly created for Min-Max Items?