You can change realmlist but it's not a good solution for a long time, something with patches different and you cant play the other region after patch.
I can't find the guide but I did it on my US client and its been playing fine for weeks. No updates yet though.
It was basicly like, make a new folder in data called enUS, put the realmlist in there.
Delete/move enGB, Cache, WTF etc. (I'd recommend making a backup)
Start the launcher and let it go.
Nope they moved it though, heres my EU directoryDid Blizz remove the Realmlist?