If you want your game to stay the exact way it is right now!:

1. Right click Europa Universalis IV in your Steam library and select Properties

2. Go to the tab called "Local Files" and press the button saying "Browse local files"

3. You should now have your "...\steamapps\common\Europa Universalis IV" folder open on your computer

4. Move/copy the entire Europa Universalis IV folder (move up one step in your directory hierarchy) to anywhere but the the steamapps-folder on your computer

5. Start the game by using eu4.exe in the folder rather than through Steam

This will prevent you from gaining any achievements whatsoever! This option is not recommended but may be desired by some. Please note that you should always have your Steam client running on your computer when playing EUIV to prevent issues with the AI and other things (You can have it in offline mode if you like, just as long as the client is running).