Employee should not be able to change SC at all
When the SC is ordered and awaiting approval, the requestor can change the details.
Also, When the approver rejects or changes the SC during approval process ,the SC is returned to the requestor with the status "In your inbox" and the requestor is again allowed to change the details with the "Change" button.
But in our implementation ,the client wants the requestor must not be able to change the SC details at all in any case after ordering .
BBP_WFL_SECURITY in PFCG for employee role has helped us partially but not completely.
We belive there should be some special task for this.