Shortly. I would like to add on_change function to categ_id field in product.product_normal_form_view.

I have something like that:

<record id="product_normal_form_view_smart" model="ir.ui.view">
        <field name="name">product_normal.form.attribute</field>
        <field name="model">product.product</field>
        <field name="inherit_id" ref="product.product_normal_form_view"/>
        <field name="arch" type="xml">
            <data>
                <xpath expr="/form/sheet/notebook" position="inside">
                        <field name="categ_id" on_change="on_change_categ_id()"/>
                </xpath>
            </data>
        </field>
    </record>

But it doesn't work, because now it adds new field. Problem is that I don't want add new field, only change existing one.

P.S. Of course I inherited product.product in py code.