Hi,

The sale.order.line tree view is embedded in the sale.order form view. If you want to modify how the product list is displayed within the Sales Order form, you need to inherit the sale.order form view.

Eg:

<record id="view_order_form_custom" model="ir.ui.view">

    <field name="name">sale.order.form.custom</field>

    <field name="model">sale.order</field>

    <field name="inherit_id" ref="sale.view_order_form"/>

    <field name="arch" type="xml">

        <!-- Modify the embedded tree view for sale.order.line -->

        <xpath expr="//notebook/page[@name='order_lines']/field/tree" position="inside">

            <!-- custom code-->

        </xpath>

    </field>

</record>

Hope it helps