Windows 8.1 Charms Bar Customizer is a freeware from door2windows which lets you easily customize the Windows 8.1 charms bar.
Apps from door2windows are truly free and DON'T include any offers to install 3rd-party apps/adware/toolbars/unwanted software and never will. The apps are portable and don't require installation.
Download door2windows App Bundledoor2windows App Bundle gives you access to all the latest apps released by door2windows in one download (along with future updates).
How to use:
Download and run the app.
The left side contains the images which are displayed when you move your mouse to one of the charms bar hot corners and the right side contains the image when you move your mouse over the charms bar.
Double-click the image that you want to change and select the new image. The app will automatically resize the image for you so it is not necessary for the image to be of specific dimensions. If you want to revert any image to the current state, right-click it.
Once you have selected all the new images, click the Change button.
The Windows Explorer will restart automatically and the new images will be displayed in the charms bar.
To revert to the original charms bar, click the Restore button.
Credit goes to Angus Johnson for the resource updater.