you can set any background from anywhere on your device, I have all my wallpapers on my mSD card in a folder specific for wallpapers as I have so many of them, you can also set the background to change on a time base you desire.... there's no need to change or add more to the windows designated wall folder...
Well, it's too bad that won't run on RT for one as it's an x86 application, and two, it's a good thing it wont run, as apparently it's loaded with malware according to the comments on that page. So the concept of RT's "walled garden" protects us from that one!here's something I think you guys might be interested in and may help
How To Set Animated Wallpaper or Video As Start Screen Background In Windows 8.1
Thanks, I knew they were in a system file somewhere. It'd be really nice if a developer made an RT store app that would allow us to change these themes with something like add-on packs.The Backgrounds are embedded in a DLL file in System32 IIRC, themeui.dll I think, I remember attempting to extract them with a Hex editor once and the were made up of a bunch of square bitmaps.