Replacers and stantalone versions require different things, and stantalone, are by nature, more difficult to make.
You first need to move the textures, and possibly rename them, so they dont overwrite existing textures. Then you need to assign those textures to the armor via NifSkope.
Add the armors to the game by duplicating existing armor and assigning the filepaths to the retextured nifs. And drop them in the world.
Making them craftable is a bit more involving and im far too lazy to do into that.