Search the executable you have created and select it. Check the 'Custom executables/arguments' option and click on 'Add another executable / arguments'. Now, go to the menu of the game on GOG Galaxy, click on Settings > Manage installation > Configure. After that, instead of replacing the original game executable with the one you have just created, you simply have to copy it to the game folder. Name it the way it pleases you most (I have named mine 'Fallout 3 mod'). If anyone is having problems to make the game launches through GOG Galaxy, just use the script provided by and transform the patch with your profile on a executable exe.file. But I got a solution and I think it is worth to share with anyone who might get stucked like I did. Italov: I ended up on this topic after installing some mods through Mod Organizer and had some problems trying to duplicate the things discussed here.