How do you backpatch wow?

Step 1: Go To Your World of Warcraft Directory
Step 2: Rename wow.exe To wowwow.exe
Step 3: Open Repair.exe
Step 4: Select Check And Repair
Step 5: Wait For It To Finish
Step 6: Once That Has Done Just Patch To The Version You Want.

I Would Use The Patch Mirrors At WoW Wiki. (Requires A Torrent Program)