Save the game at the start of this. You can make a manual game save at the start of the chapter by opening the pause menu and going down to save. You should make 2 as the auto save may override one of them preventing you from being able to reload. It will be much easier if you wait until a second run before attempting this as you will have learned how to get through the mission as easy as possible. If you get caught you can reload your game save and try again.
Get through Scotland cemetery combat encounter without killing or being seen