<odoo>
    <data>
        <!-- Wrap the default in if/else to display custom content based on a custom variable. $0 will contain the original. -->
        <template id="external_layout_standard_custom" inherit_id="web.external_layout_standard">
            <xpath expr="//img[@t-if='company.logo']" position="replace">
                <t t-if="custom_header">
                    <h2>CUSTOM LOGO HERE</h2>
                </t>
                <t t-else="1">$0</t>
            </xpath>
        </template>

        <!-- Just set the custom variable in the report you need before external_layout is called -->
        <template id="report_saleorder_custom" inherit_id="sale.report_saleorder">
            <xpath expr="//t[@t-call='web.html_container']" position="before">
                <t t-set="custom_header" t-value="True"/>
            </xpath>
        </template>

        <!-- That's it! -->

        <!-- Should work the same for new reports too -->
        <template id="report_saleorder_commercial">
            <t t-set="custom_header" t-value="False"/>
            <t t-call="web.html_container">
                <t t-set="is_commercial" t-value="True"/>
                <t t-foreach="docs" t-as="doc">
                    <t t-call="sale.report_saleorder_document" t-lang="doc.partner_id.lang"/>
                </t>
            </t>
        </template>
        <report
            id="action_report_commercial_invoice"
            string="Commercial Invoice"
            model="sale.order"
            report_type="qweb-pdf"
            file="beyondled.report_saleorder_commercial"
            name="beyondled.report_saleorder_commercial"
            print_report_name="'Commercial Invoice - %s' % (object.name)"
        />
    </data>
</odoo>