Empire Total War
Download ETF21.zip, unzip it, run ETF21.exe and install the mod following the on screen instructions. Make sure that you install the mod in your game's directory which by default is C:\Program Files (x86)\Steam\steamapps\common\empire total war. If you have installed the game in a different path, redirect the installer when the installation path screen appears, browsing your path.
Always start Steam manually and then start ETF using the desktop shortcut. Select your campaign and play. No command is needed to be added in user.empire_script.txt.
You can uninstall the mod using add\remove programs in windows. If you accepted it during installation, there will be a folder created in the Start Menu, named Empire Total Factions containing a uninstall link. Uninstall exe can be found in game's directory (...\empire total war\).