copy the whole wow folder paste it in whatever drive (yes it can be same drive). Rename the folder to whatever, i just renamed wow.exe in case. Installed WOTLK, this only affected the original folder. "Get High, Rule The World."
You dont let blizzard updater update it... you have to download and updater from a website such as "filefront" if you need the links i can provide them, i can also provide a link to a full 2.4.3 WoW but it is GB but it wont afect anything. Being a Black Hat never felt so good!
You do not have to download anything. just get rid of that line and you should be fine. And if it still wants to patch for some odd reason you have another launcher in your wow folder its called WOW.exe just use that is skips the launcher part and puts you directly to the login page. So no patching