MoP has made a complete fucking mess of changing region, and it's a lot more involved than simply editing a text file, because the launcher seems to be getting the region from so many different files now, that you have to delete them all.
To convert from one region to another (in this example from enUS), make sure you've set your computer to display hidden system folders, hidden files, and hidden file extensions (the menu for this can be found using
[1] for XP, or
[2] for vista/7), then delete:
- World of Warcraft Launcher.exe inside ...\World of Warcraft\
- .agent.db inside ...\World of Warcraft\
- \Cache folder inside ...\World of Warcraft\
- \enUS folder inside ...\World of Warcraft\Data\ (or whatever folder matches your region)
For Windows 7 delete:
- \Battle.net folder inside C:\ProgramData\
For windows XP delete:
- \Battle.net folder inside either C:\Documents and Settings\All Users\Application Data\ or C:\Documents and Settings\<your username>\Application Data\ (delete both if you find them)
Log in to battle.net for the region you want to change to (you can log into either us.battle.net or eu.battle.net with the same F2P account name).
Click the blue 'Account' button next to the 'login' button.
Click the 'Download Game Clients' button under the big green 'Add a Game Key' button.
Download the 'Full Game client' (it's actually the same file as the starter edition). It's a 118MB download.
Run the World-of-Warcraft-Setup-[region].exe file, and if you changed from the default location before, tell it to install to wherever the World of Warcraft folder is (it'll add 'World of Warcraft' to the end of any folder you point it at, so point it at the one with World of Warcraft in it). Tell it you've already activated when it asks.
It won't need to do a full install, as it can use most of the files from the other region, but you still need to do an over 1GB download.
Note that there isn't a realmlist.wtf file anywhere in the new install, showing that the game isn't using one any more.
It's probably a better idea to make a copy of your WoW folder, do the above to it, and then have 2 installs, to save having to do this every time you want to switch.