How do I add new paths to DN3D?

dl.dropboxusercontent.com/u/14499652/Duke3D/multiplayer_guide.html

You can change the "path" in the properties dialogue for the shortcut. I recommend creating a new shortcut instead if that works. I've never tried Duke Nukem 3D over multiplayer. The eDuke port has a warning in the wiki about multiplayer possibly being buggy or broken depending on which build you use.