• Go to the CRM app

• Open an opportunity and go to the from view (debug mode) 

• go to you inherited views - copy and past that code:  

<xpath expr="//field[@name='partner_is_blacklisted']/..//field[@name='partner_id']" position="attributes">

    <attribute name="options">{'no_create_edit': True}</attribute>

 </xpath>

• 
  

• go to a lead and copy past that code to the inherited view

<xpath expr="//field[@name='partner_id']" position="attributes">

    <attribute name="options">{'no_create_edit': True}</attribute>

 </xpath>

• Finally: pay attention to the access rights you give - if you don't want that one user can create a contact you don't have to just put him away of the contact creation from the extra rights. You also have to go to the access rights details (debug mode - top right). Sort by object and then take him off from creation and delete rights of each contact object.