Thank you @Ray! That is fantastic.

I must replace

<template id="message_notification_email">

<div>

<div t-if="has_button_access" itemscope="itemscope" itemtype="http://schema.org/EmailMessage">

<div itemprop="potentialAction" itemscope="itemscope" itemtype="http://schema.org/ViewAction">

<link itemprop="target" t-att-href="button_access['url']"/>

<link itemprop="url" t-att-href="button_access['url']"/>

<meta itemprop="name" t-att-content="button_access['title']"/>

</div>

</div>

<div t-if="has_button_access or len(actions) &gt; 0 or not is_discussion"

summary="o_mail_notification" style="padding: 0px; width:600px;">

<table cellspacing="0" cellpadding="0" border="0" style="width: 600px; margin-top: 5px;">

<tbody><tr>

<td valign="center">

<a t-if="has_button_access"

t-att-href="button_access['url']"

style="padding: 8px 12px; font-size: 12px; color: #FFFFFF; text-decoration: none !important; font-weight: 400; background-color: #875A7B; border: 0px solid #875A7B; border-radius:3px">

<t t-esc="button_access['title']"/>

</a>

<t t-if="actions">

<t t-foreach="actions" t-as="action">

|

<a t-att-href="action['url']" style="color: #875A7B; text-decoration:none !important;">

<t t-esc="action['title']"/>

</a>

</t>

</t>

</td>

<td valign="center" align="right">

<img t-att-src="'/logo.png?company=%s' % company.id" style="padding: 0px; margin: 0px; height: auto; max-width: 200px; max-height: 36px;" t-att-alt="'%s' % company.name"/>

</td>

</tr><tr>

<td colspan="2" style="text-align:center;">

<hr width="100%"

style="background-color:rgb(204,204,204);border:medium none;clear:both;display:block;font-size:0px;min-height:1px;line-height:0; margin:4px 0 12px 0;"/>

<p t-if="subtype.internal" style="background-color: #f2dede; padding: 5px; margin-bottom: 16px;">

<strong>Internal communication</strong>: Replying will post an internal note. Followers won't receive any email notification.

</p>

</td>

</tr></tbody>

</table>

</div>

<div t-raw="message.body"/>

<ul t-if="tracking_values">

<t t-foreach="tracking_values" t-as="tracking">

<li><t t-esc="tracking[0]"/>: <t t-esc="tracking[1]"/> -&gt; <t t-esc="tracking[2]"/></li>

</t>

</ul>

<div t-if="signature" t-raw="signature" style="font-size: 13px;"/>

<p style="color: #555555; margin-top:32px;">

Hallo

<span t-if="company.name">

by

<a t-if="website_url" t-att-href="website_url" style="text-decoration:none; color: #875A7B;">

<span t-esc="company.name"/>

</a>

<span t-if="not website_url" t-esc="company.name"/>

</span>

using

<a target="_blank" href="https://www.odoo.com?utm_source=db&amp;utm_medium=email" style="text-decoration:none; color: #875A7B;">Odoo</a>.

</p>

</div>

</template>

<template id="mail_notification_borders">

<div>

<table border="0" width="100%" cellpadding="0" bgcolor="#ededed" style="padding: 20px; background-color: #ededed; border-collapse:separate;" summary="o_mail_notification">

<tbody>

<!-- HEADER -->

<tr>

<td align="center" style="min-width: 590px;">

<table width="590" border="0" cellpadding="0" bgcolor="#875A7B" style="min-width: 590px; background-color: rgb(135,90,123); padding: 20px; border-collapse:separate;">

<tr><td valign="middle">

<span style="font-size:20px; color:white; font-weight: bold;">

<t t-esc="message.record_name"/>

</span>

</td><td valign="middle" align="right">

<img t-att-src="'/logo.png?company=%s' % company.id" style="padding: 0px; margin: 0px; height: auto; width: 80px;" t-att-alt="'%s' % company.name"/>

</td></tr>

</table>

</td>

</tr>

<!-- CONTENT -->

<tr>

<td align="center" style="min-width: 590px;">

<table width="590" border="0" cellpadding="0" bgcolor="#ffffff" style="min-width: 590px; background-color: rgb(255, 255, 255); padding: 20px; border-collapse:separate;">

<tbody><td valign="top" style="font-family:Arial,Helvetica,sans-serif; color: #555; font-size: 14px;">

<t t-raw="message.body"/>

</td></tbody>

</table>

</td>

</tr>

<!-- FOOTER -->

<tr>

<td align="center" style="min-width: 590px;">

<table width="590" border="0" cellpadding="0" bgcolor="#875A7B" style="min-width: 590px; background-color: rgb(135,90,123); padding: 20px; border-collapse:separate;">

<tr><td valign="middle" align="left" style="color: #fff; padding-top: 10px; padding-bottom: 10px; font-size: 12px;">

<t t-esc="company.name"/><br/>

<t t-esc="company.phone"/>

</td><td valign="middle" align="right" style="color: #fff; padding-top: 10px; padding-bottom: 10px; font-size: 12px;">

<t t-if="company.email">

<a t-att-href="'mailto:%s' % company.email" style="text-decoration:none; color: white;"><t t-esc="company.email"/></a><br/>

</t>

<t t-if="company.website">

<a t-att-href="'%s' % company.website" style="text-decoration:none; color: white;">

<t t-esc="company.website"/>

</a>

</t>

</td></tr>

</table>

</td>

</tr>

<tr>

<td align="center" style="padding: 8px; font-size:11px;">

Powered by <a target="_blank" href="https://www.odoo.com?utm_source=db&amp;utm_medium=email">Odoo</a>.

</td>

</tr>

</tbody>

</table>

</div>

</template>

with

<xpath expr="//t[1]/div[1]/table[1]/tbody[1]/tr[4]" position="replace"/>

Is this right?

Sorry for the question. :D

Before the next lenghty comment, please make yourself familiar with the basics about view inheritance and xpath.

Thank you for the great Supportansprüchen helpfully comment!

Bad if a community forum consists only of service providers.

you may also want to customize also the fallowing views:

1. livechat_email_template

2. mail.mail_notification_paynow

This totally works!

Best answer found so far, thanks Ray.
If you don't know much about xpath (like I do), you can use a xpather render (like http://xpather.com/) to help you to identify what you are updating.

Thanks Yuan!! See - https://twitter.com/ray_odoo/status/1456051367005413376