The tutorials at http://hotpot.uvic.ca/tutorials6.php are a good starting point for your own modifications.
You'll be required to work with code: xHTML, CSS and sometimes Javascript. This means that you have familiarized yourself with the "Hacking workshops" and know what and which files we are referring to.
So check these out:
The tutorials you'll find on this site are both simple tricks and more complex code implementations to bring more interactivity into the exercises created with HotPotatoes v6 as well as using HotPotatoes in Moodle.