Detailed explanation
iTunesStoreX hooks to the iTunesStore framework (com.apple.itunesstore), which is responsible for making network requests to Apple's iTunes services. It hooks to it, and changes the initialization bag's endpoint from http://ax.init.itunes.apple.com, which has been misconfigured by apple most likely, and only returns "Not allowed" instead of the actual bag. Instead of using this endpoint, it gets redirected to https://init.itunes.apple.com, an endpoint that was used since iOS 7 Beta 4 instead of the old one, and is still used to this day by devices accessing the iTunes Store.
The store layout is fixed by redirecing the .js dependencies of the HTML store frontend on-the-fly to ones that aren't broken, yet still hosted by apple.