Updating the Power Store is definitely a custom endeavor since it is designed to work out of the box any edits that you make could alter the functionality of the site in an unintended way.
It is possible though to update the PowerStore with the various WebAssist tools. When it comes to this currency support that you would like to add please explain a little about what you are hoping to achieve as an end result and I can try to give you some pointers for the tools and direction based on that.