price_security/views/sale_view.xml

<?xml version="1.0"?>
<openerp>
    <data>
        <!-- sale.order -->
        <record id="view_price_security_order_form" model="ir.ui.view">
            <field name="name">price_security.order.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="groups_id" eval="[(6, 0, [ref('group_restrict_prices')])]"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='order_line']/form" position="inside">
                    <field name="product_can_modify_prices" invisible="1"/>
                </xpath>
                <xpath expr="//field[@name='order_line']/tree" position="inside">
                    <field name="product_can_modify_prices" invisible="1"/>
                </xpath>

                <!-- add readonly price unit on tree -->
                <xpath expr="//field[@name='order_line']/tree//field[@name='price_unit']" position="after">
                    <field name="price_unit_readonly" attrs="{'readonly': [('product_can_modify_prices','=', False)]}"/>
                </xpath>
                <!-- make price unit invisible on tree -->
                <xpath expr="//field[@name='order_line']/tree//field[@name='price_unit']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>

                <!-- add readonly tax on tree -->
                <xpath expr="//field[@name='order_line']/tree//field[@name='tax_id']" position="after">
                    <field name="tax_id_readonly" attrs="{'readonly': [('product_can_modify_prices','=', False)]}" domain="[('parent_id','=',False),('type_tax_use','&lt;&gt;','purchase')]" widget="many2many_tags"/>
                </xpath>
                <!-- make tax invisible on tree -->
                <xpath expr="//field[@name='order_line']/tree//field[@name='tax_id']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>

                <!-- add readonly price unit on form -->
                <xpath expr="//field[@name='order_line']/form//field[@name='price_unit']" position="after">
                    <field name="price_unit_readonly" attrs="{'readonly': [('product_can_modify_prices','=', False)]}"/>
                </xpath>
                <!-- make price unit invisible on form -->
                <xpath expr="//field[@name='order_line']/form//field[@name='price_unit']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>

                <!-- add readonly tax on form -->
                <xpath expr="//field[@name='order_line']/form//field[@name='tax_id']" position="after">
                    <field name="tax_id_readonly" attrs="{'readonly': [('product_can_modify_prices','=', False)]}" domain="[('parent_id','=',False),('type_tax_use','&lt;&gt;','purchase')]" widget="many2many_tags"/>
                </xpath>
                <!-- make tax invisible on form -->
                <xpath expr="//field[@name='order_line']/form//field[@name='tax_id']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>
            </field>
        </record>
        
    </data>
</openerp>