Of course, that makes sense. However, there are also mods like that one: http://www.nexusmods.com/fallout3/mods/17149/?tab=1&navtag=http%3A%2F%2Fwww.nexusmods.com%2Ffallout3%2Fajax%2Fmoddescription%2F%3Fid%3D17149%26preview%3D&pUp=1 That requires user to own another game and extract files from it. However it works much better as replacer, since, well.. it does not replace anything. So, it's like it's esp/esm only, right?