Owen let us know that they just released a free wallpaper changer for the BlackBerry running OS 4.7+. This type of applications give your BlackBerry a new look every time the wall paper changes.
The application is free and you can download directly to you BlackBerry at this link.
Here is a description from the developer along with desktop install process:
Wallpaper Shifter is a smart tool enables your BB to change wallpaper automatically, you can define a folder and desired interval at the same time.
* Only support 4.7 or above OS
How to install:
To install Wallpaper Shifter, download the install files to your PC. Connect your phone to your PC, open your BlackBerry device manager, click Application Loader. Choose WallpaperShifter.alx and install. Reboot your phone and you can find Wallpaper Shifter in Download.