sale_view.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  product customer code for OpenERP
  Copyright (C) 2013 Agile Business Group sagl (<http://www.agilebg.com>).
    Authors, Nicola Malcontenti, nicola.malcontenti@agilebg.com
  The licence is in the file __openerp__.py
-->
<openerp>
    <data>

        <record id="view_order_form" model="ir.ui.view">
            <field name="name">sale.order.product.code.view.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field eval="16" name="priority"/>
            <field name="arch" type="xml">
                <xpath expr="//form//tree//field[@name='product_id']" position="after">
                    <field name="product_customer_code"/>    	
                </xpath>
                <xpath expr="//form//form//field[@name='product_id']" position="after">
                    <field name="product_customer_code"/>    	
                </xpath>
            </field>
        </record>

    </data>
</openerp>