sale_view.xml

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

<!--
    Copyright (C) 2014 Akretion (http://www.akretion.com/)
    @author Alexis de Lattre <alexis.delattre@akretion.com>
    The licence is in the file __openerp__.py
-->

<record id="view_order_form" model="ir.ui.view">
    <field name="name">fiscal.position.update.sale.order.form</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form"/>
    <field name="arch" type="xml">
        <field name="fiscal_position" position="attributes">
            <attribute name="on_change">fiscal_position_change(fiscal_position, order_line, context)</attribute>
        </field>
    </field>
</record>

</data>
</openerp>