pms/hotel_door_codes/views/inherit_hotel_property.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <!-- Hotel Property Settings -->
    <data>
        <!-- Inherit Property view to add 'door_code' -->
        <record id="door_code_view_property_form" model="ir.ui.view">
            <field name="name">door_code.config.view_property_form</field>
            <field name="model">hotel.property</field>
            <field name="inherit_id" ref="hotel.hotel_property_views_form"/>
            <field name="arch" type="xml">
                <xpath expr="//page[@name='hotel_settings']" position="inside">
                    <group colspan="4" col="4" name="door_codes" string="Door Codes">
                        <field name="precode"/>
                        <field name="postcode"/>
                    </group>
                </xpath>
            </field>
        </record>
    </data>
</odoo>