7 Ubercart hook_order for PayPal Paments Pro payment received
IMHO the easiest way is to use Rules. There's a default rule you can clone and tune for your needs: uc_payment_received.

I would clone that rule, add the condition to ensure it's a payment coming from PayPal, then replace the action with "Send an order email". The you should be able to customize the email.

Writing a custom module for this task is a bit overkill.