company_set_information/company_set_information_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record model="ir.ui.view" id="res_company_form_view_ruc">
            <field name="name">res.company.form.view.ruc</field>
            <field name="model">res.company</field>
            <field name="inherit_id" ref="base.view_company_form" />
            <field name="arch" type="xml">
                <field name="company_registry" position="after">
                    <field name="company_ruc"/>
                    <field name="legal_agent"/>
                    <field name="agent_ruc"/>
                    <field name="exportador" required="1"/>       
                </field>
            </field>
        </record>
    </data>
</openerp>