For now, To use different UI's for different charecters; You'd have to logout and exit the game.. Change the INI.. Load up again and login as different charecter..
After they fix the /LoadUI Command and get the settings saving correctly.. The INI file won't be needed unless you want a modded Patcher/Login screen.. At least that's how it was in EQ1
edit: Heh, I must be a slow typer...