sale_restrict_price_c/security/restrict_saleprice_c.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
   <data>
        <record id="groups_restrict_price_c" model="res.groups">
            <field name="name">Permitir vender por debajo del precio C</field>
            <field name="category_id" ref="base.module_category_extra" />
        </record>

    </data>
  </openerp>