Change and test the default and any Opencart (opensource webshop system) order notification email template without make a new order again.
The time is money and your life could be easier.
Create a brand new folder under your Opencart root directory. for example: test
Copy the four files and the output folder to it.
Select an existing order number from your webshop or create a new order using your webshop interface like a customer.
Set the order number in start.php file and run using the command line interface.
See the result in the output folder. (generated html file)
Open the file in a webbrowser and change it as you want.