pos/pos_order_pricelist_change/view/view.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- ********************************************************************** -->
<!--Point Of Sale - Order Pricelist Change for Odoo                         -->
<!--Copyright (C) 2014 GRAP (http://www.grap.coop)                          -->
<!--@author Sylvain LE GAL (https://twitter.com/legalsylvain)               -->

<!--This program is free software: you can redistribute it and/or modify    -->
<!--it under the terms of the GNU Affero General Public License as          -->
<!--published by the Free Software Foundation, either version 3 of the      -->
<!--License, or (at your option) any later version.                         -->

<!--This program is distributed in the hope that it will be useful,         -->
<!--but WITHOUT ANY WARRANTY; without even the implied warranty of          -->
<!--MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           -->
<!--GNU Affero General Public License for more details.                     -->

<!--You should have received a copy of the GNU Affero General Public License-->
<!--along with this program.  If not, see <http://www.gnu.org/licenses/>.   -->
<!-- ********************************************************************** -->
<openerp>
    <data>
    <!-- View : pos.order -->
        <record id="view_pos_order_form" model="ir.ui.view">
            <field name="name">pos.order.form</field>
            <field name="model">pos.order</field>
            <field name="inherit_id" ref="point_of_sale.view_pos_pos_form" />
            <field name="arch" type="xml">
                <header position="inside">
                    <button name="action_recompute_pricelist" string="Recompute With Pricelist"  type="object" states="draft"/>
                </header>
                <field name="pricelist_id" position="attributes">
                    <attribute name="on_change">onchange_pricelist_id(pricelist_id, lines)</attribute>
                </field>
            </field>
        </record>

    </data>
</openerp>