Actually if you just have to add one field, I find it way less complicated to just edit the original xml files. For instance, if you want to add the reference field to the list view of the sale orders: just edit sale_view.xml under the sale module (Openerp/server/server/openerp/addons/sale) and add your field.
Example:
<tree string="Sales Orders" fonts="bold:message_unread==True" colors="grey:state=='cancel';blue:state in ('waiting_date','manual');red:state in ('invoice_except','shipping_except')">
<field name="message_unread" invisible="1"/>
<field name="name" string="Order Number"/>
<field name="date_order"/>
<field name="partner_id"/>
<field name="user_id"/>
<field name="client_order_ref"/>
<field name="amount_total" sum="Total Tax Included"/>
<field name="state"/>
</tree>
</field>
</record>
<record id="view_quotation_tree" model="ir.ui.view">
<field name="name">sale.order.tree</field>
<field name="model">sale.order</field>
<field name="priority">4</field>
<field name="arch" type="xml">
<tree string="Quotation" fonts="bold:message_unread==True" colors="grey:state=='cancel';blue:state in ('waiting_date','manual');red:state in ('invoice_except','shipping_except')">
<field name="message_unread" invisible="1"/>
<field name="name" string="Quotation Number"/>
<field name="date_order"/>
<field name="partner_id"/>
<field name="user_id"/>
<field name="client_order_ref"/>
<field name="amount_total" sum="Total Tax Included"/>
<field name="state"/>
If you take this approach for the list view, adding "<field name="client_order_ref"/>" in between the existing fields will be sufficient. No other parameters have to be adjusted.
Have add this field successfully.