How to place a Custom Message at Checkout End?

-- HikaShop version -- : 2.2.2
-- Joomla version -- : 2.5.16
-- PHP version -- : 5.3.27

I need some guidance. I sell digital products using Hikashop. I just recently upgraded from Starter to Hikashop Essential. How do I add a custom message at the end of the purchase process, similar to the message I receive after I purchased Hikashop Essential (see the attached image)?

Basically, I want to place a message that tells the customer that they can access the downloads via a link on the menu, and if their order is not confirmed automatically to please use the contact form to request confirmation.

Hi,
The best solution will probably be to add your message through the "End" file of your checkout view, of your front-end template through "Hikashop->Display->Views".

OK. I will try that, and see how it works out. However, I do have two questions:

1. Will the changes I make be undone when I update Hikashop to the next latest version when it comes out?
2. Is this the method the Hikashop team used to get that message to be displayed at the end of purchasing Hikashop Essential?