How can I change opencart order email content as our wish? Is it possible?

if you just want to change powered by link then go to

catalog\language\english\mail\order.php

and change it.

You can do the changes by visiting the following model/view files.

References are as:

1. ..\catalog\view\theme\default\template\mail\order.tpl (to doinvoice template structural or data updates)

2. ..\catalog\model\checkout\order.php (to retrieve/send any data value to order invoice template.)

3. ..\catalog\language\english\mail\order.php (to add more language variables or any custom update.)

Hope this is useful.

Thanks!

Yes of course it's possible. You can modify the content by editing the following template file:

/catalog/view/theme/default/template/mail/order.tpl

(assuming that you are using the default template)

But if you want to modify the subject and other stuff, you'll need to edit the order Model file:

/catalog/model/checkout/order.php

then find

$mail->setSubject($subject);

and set the $subject to whatever you want :)