Create a text document with this inside, changing the directories to your choosing.
Code:
@echo OFF
cls
del "D:\UIBackup\AddOns\" /y
del "D:\UIBackup\WTF\" /y
xcopy "D:\Program Files\World of Warcraft\Interface\AddOns\*.*" "D:\UIBackup\AddOns\*.*" /e /v /y
xcopy "D:\Program Files\World of Warcraft\WTF\*.*" "D:\UIBackup\WTF\*.*" /e /v /y
echo Backup Complete.
Change the file extention to '.bat' from '.txt' and open to run the backup.
Alternatively, you can have this run when you shutdown your computer or on a schedule using
Windows Scheduled Tasks.