First, if you were such a bad ass programmer, you would have figured this much out by now. Second, if you want any information on how those files are used, dissassemble the xex with IDA Pro. From there you have the whole blueprint for the game engine, which will tell you more than a hex editor, or any of us on this forum. The only reason skyrim has mods like this on the 360 is because the game came out on the PC with a homebrew mod options. Since it is the same game, compiled for a different CPU, modders already know what is up with the files. If you could find a PC version of the game, and you can find tools to do this for that version of the games, and then might be able to take what you learn there and apply it to the 360 version.
Personally for what you are trying to do, a Nintendo Switch, with LayeredFS(CFW Option), would be a better option, as it is designed primarilly for this sort of application. Unfortunatly the xbox doesnt do this. On top of that some game developers pre-compile assets(Hince why we needed the aurora asset editor) into d3d maps, because it is faster than loading an image file, and having the console convert it into a d3d map to load. Once again this is a development choice, and every developer is different about how they write code. I have seen many code implementations that are all different, but essentially do the same thing over the years. This applies to all programmes, so until you step through the dissassembled XEX, and spend way more time then you want looking at that code, you wont have the first idea of what to do.