res_users.xml

<?xml version="1.0"?>
<!--
    Copyright (C) 2016-Today: La Louve (<http://www.lalouve.net/>)
    @author: Sylvain LE GAL (https://twitter.com/legalsylvain)
    License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
-->

<odoo>
    <record model="res.users" id="base.user_root">
        <field name="barcode">123</field>
    </record>

    <record model="res.users" id="base.user_demo">
        <field name="barcode">456</field>
    </record>

</odoo>