SUS - MM Scenario: Hide buttons / functionalities in SUS interface

Hi,

we're in SUS-MM scenario and we'd like, in the Response phase of the PO,

1) not allow the Supplier to reject the entire PO or some positions of the PO;

2) also we'd need not to allow the Supplier to modify Price information related to the PO positions during the PO.

My question is: how can we 'hide' those buttons / functionalities in the SUS interface?

Thanks