You can just copy your WoW folder again to have an additoinal one as they have no registery settings. I have 3 different WoW folders.

Folder 1 - Main Client, max settings for raiding and pvping on my main.
Folder 2 - Master Client, moderately high settings at about 75% of the normal running with minimal addons.
Folder 3 - Slave Client, minimal settings ran at around 25% of normal with only addons required for my multiboxing needs.