Windows hides windows store apps in c:/users/YourUserName/AppData(hidden folder)/Local/Packages
I'm not sure if there are any additional complications relevant to modifying files in windows store apps. It would be very Microsoft if there were.
As with others here, I recommend using the normal windows installer version, or the portable version, instead of the windows store version. There have been a number of issues with the windows store version, and it doesn't offer any benefits over the traditional installers