Change "system" edit buttons?

They are displayed at the top of the view files.
You can edit them via the menu Display->Views.

For example, for the order details page, it's the file "show" of the view "order" of the front end :
<div class="toolbar hikashop_header_buttons" id="toolbar">
<table>
<tr>
<?php if(hikashop_level(1) && $this->config->get('print_invoice_frontend')){ ?>
<td>
<a class="modal" rel="{handler: 'iframe', size: {x: 760, y: 480}}" href="<?php echo hikashop_completeLink('order&task=invoice&order_id='.$this->element->order_id,true); ?>">
<span class="icon-32-print" title="<?php echo JText::_('PRINT_INVOICE'); ?>">
</span>
<?php echo JText::_('HIKA_PRINT'); ?>
</a>
</td>
<?php } ?>
<td>
<a onclick="submitbutton('cancel'); return false;" href="#" >
<span class="icon-32-back" title="<?php echo JText::_('HIKA_BACK'); ?>">
</span>
<?php echo JText::_('HIKA_BACK'); ?>
</a>
</td>
</tr>
</table>
</div>