Extract the folder in the archive either where Musicbee is installed or in the skins directory, and execute the batch file in the icons directory afterwards. It may or may not require Administrator privileges to complete successfully, but I'd run it that way just to be sure.
When it asks you to verify the path displayed, then just make sure that it's the same as the folder the batch is running.
Make sure you don't have any file transfers running when you execute the batch, since it restarts explorer.exe to save you from the trouble or logging in and out or doing it manually.
Deleting, renaming or moving the files after installation will make the icons disappear. Running the batch without all the icons will result in the missing icons replaced by a Windows unknown filetype icon. In any case, to restore the original icons, just start Musicbee with Administrative privileges and re-apply file associations from Preferences -> General.
This batch is provided without any guarantee express or implied, and you assume all responsibility in case of computer damage, relationship problems, sterility or unemployment resulting from it's use.