Magento – Change “subtotal” label in Sales Order Email

To send different order conformation email depending on specific criteria you would either have to :

1. Rewrite sendNewOrderEmail() in Mage_Sales_Model_Order and add logic to check the template

2. Disable magento "order confirmation email" in system config, then create a custom module to send your email by coping logic from sendNewOrderEmail() using event/observer

3. For simple text changes, you could use template logic {{if order.customer_group_id}} or {{depend order.customer_group_id}} but they seem to only evaluate true/false condition, therefore for more advance logic you could include a block

{{block type='core/template' area='frontend' template='sales/custom_logic.phtml' order=$order}}

In custom_logic.phtml

<?php
  $order = $this->getOrder()

  if($order->getCustomerGroupId() == 1){
     ///do
   ....

See Magento Email Template If Statements

The easiest way is to rewrite the Mage_Sales_Model_Order class in your own extension adding the function getShippingDescription which is called in the email template (see below)

<td valign="top" style="font-size:12px; padding:7px 9px 9px 9px; border-left:1px solid #EAEAEA; border-bottom:1px solid #EAEAEA; border-right:1px solid #EAEAEA;">
   {{var order.getShippingDescription()}}
   &nbsp;
</td>

The new getShippingDescription method would return a block instance from your module that has the modifications you want.

your rewritten Sales Order class app/code/[codepool]/[Namespace]/[Module]/Model/Sales/Order.php

class [Namespace]_[Module]_Model_Sales_Order extends Mage_Sales_Model_Order
{
   public function getShippingDescription()
   {
      return Mage::app()->getLayout()->createBlock('core/template')->setTemplate('path/to/your/file.phtml')->toHtml();
   }
}