Use on a custom firmware (CFW) Switch (like Atmosphere).
Depending on what "feature" you want to add, you have two main paths: Lil Gator Game (NSP)(Update 1.0.1).rar
Place your modified files in atmosphere/contents/[TitleID]/romfs/ . The game will load your new features instead of the original ones when it boots. Use on a custom firmware (CFW) Switch (like Atmosphere)