Go to redist, not in to custom_stories, but in to maps, in the maps folder you create a new folder named the_tunnel and inside of that folder you place the map and hps for the map.
When you wanna try the map as regular in the game, you gotta change everything back in both the user_settings and main_settings, and place the maps back in to custom_story.
Because it's annoying to change the user_settings, I advice you to create 2 Amnesia Main folders, one for gamin and one for development (Tanshaydar who came up with this idea). In the gamin one you leave the settings as they've always been, and in the one with development you change the user and main settings to dev enviroment settings! So whenever you wanna play you change the map name to Main and the development one to MainD and vice versa