res_company.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>

        <record model="ir.ui.view" id="view_company_form">
            <field name="name">res.company.form (l10n_lu_ext)</field>
            <field name="model">res.company</field>
            <field name="inherit_id" ref="base.view_company_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='vat']" position="before">
                    <field name="l10n_lu_matricule" attrs="{'invisible': [('country_id', '!=', %(base.lu)d)]}"/>
                </xpath>
            </field>
        </record>

    </data>
</openerp>