Screen Varient for the Invoices pricing Conditions

Dear All,

I got a requirement that in the VF01 or VF02, The User should not be able change any pricing condition which was copied from the Sales Order.

Normally pricing would be done mannualy in the Sales Order and currently there is no restriction and the User can delete the Pricing Conditions.

Please tell me how to control this using the screen varient.

Thank U

U..