Rajahs of India is being released this week, and if you are on Steam, your game will be auto-updated. If you want to continue to play Lux Invicta while the Regency Council works to get LI working with the new patch, you'll need to backup your game folder before Wednesday.
To do this, navigate to your Steam common folder (normally Program Files (x86)\Steam\SteamApps\common on 64 bit systems, or Program Files\Steam\SteamApps\common on 32 bit systems), select the Crusader Kings II folder within it, and copy it (CTRL-C or right click->copy) then navigate where you want to save it and paste it (CTRL-V or right-click->paste).
To do this, navigate to your Steam common folder (normally Program Files (x86)\Steam\SteamApps\common on 64 bit systems, or Program Files\Steam\SteamApps\common on 32 bit systems), select the Crusader Kings II folder within it, and copy it (CTRL-C or right click->copy) then navigate where you want to save it and paste it (CTRL-V or right-click->paste).