For those who want to "downgrade" their Patch to 2.3.0:
Go into your WoW Folder. For example "C:\World of Warcraft\
Switch into the Data Folder. Example: "C:\World of Warcraft\Data\
Now delete the File called "patch.MPQ". Now go back into your WoW Folder and click "Repair.exe".
Leave all how it is and push the button called "Set back to default and scan" or something. I dunno the exact button name in English because I am using the german version =)
Your WoW should be patched to the first Version of World of Warcraft now.
Now press Launcher.exe in your WoW Folder and let the Autopatcher patch your Version to 2.3.0 but be careful and cancel the update after 2.3.0 is installed.
P.S.: If you use WOW.exe in your WoW Folder, your Game Client will not be autopatched ;-)
Regards from Germany...