{% extends "admin/change_form.html" %}
{% load i18n %}

{% block object-tools %}
{% if change %}{% if not is_popup %}
<form id="resend-email" method="POST" action="{% url "shop_invoice_resend" object_id %}?next={{ request.path }}">
    {% csrf_token %}
</form>
<ul class="object-tools">
    {% if has_pdf %}
    <li><a href="{% url "shop_invoice" object_id %}?format=pdf">{% trans "Download PDF invoice" %}</a></li>
    {% endif %}
    <li><a href="#" onclick="document.getElementById('resend-email').submit(); return false;">{% trans "Re-send order email" %}</a></li>
    <li><a href="history/" class="historylink">{% trans "History" %}</a></li>
</ul>
{% endif %}{% endif %}
{% endblock %}

{% extends "admin/change_form.html" %}
{% load i18n %}

{% block object-tools %}
{% if change %}{% if not is_popup %}
<form id="resend-email" method="POST" action="{% url "shop_invoice_resend" object_id %}?next={{ request.path }}">
    {% csrf_token %}
</form>
<ul class="object-tools">
    {% block object-tools-items %}
    {% if has_pdf %}
    <li><a href="{% url "shop_invoice" object_id %}?format=pdf">{% trans "Download PDF invoice" %}</a></li>
    {% endif %}
    <li><a href="#" onclick="document.getElementById('resend-email').submit(); return false;">{% trans "Re-send order email" %}</a></li>
    <li><a href="history/" class="historylink">{% trans "History" %}</a></li>
    {% endblock %}
</ul>
{% endif %}{% endif %}
{% endblock %}

Add object-tools-items block to order admin template
Add object-tools-items block to order admin template
