multi_store_partner/views/res_partner.xml

<?xml version="1.0"?>
<openerp>
    <data>

        <!-- Res Partner Form -->
        <record id="view_res_partner" model="ir.ui.view">
            <field name="name">res.partner.form</field>
            <field name="model">res.partner</field>
            <field name="inherit_id" ref="base.view_partner_form"/>
            <field name="arch" type="xml">
                <field name="user_id" position="after">
                    <field name="store_id" groups="multi_store.group_multi_store" string="Sucursal" placeholder="Sucursal"/>
                </field>                
            </field>
        </record>
        
    </data>
</openerp>