eiru_inmobiliaria/views/account_invoice.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
  <data>
    <record model="ir.ui.view" id="invoice_form">
       <field name="name">invoice_form</field>
       <field name="model">account.invoice</field>
       <field name="inherit_id" ref="account.invoice_form"/>
       <field name="arch" type="xml">
          <field name="number" position="after">
            <field name="cuotas" readonly="1"/>
          </field>
          <field name="origin" position="replace">
            <field name="origin" readonly="1"/>
          </field>
      </field>
    </record>
</data>
</openerp>