DirectXTex VS DuckX

Optimized Vanilla Textures were optimized for PC and then ported to console. They were optimized using an 'optimizer' for Skyrim, which was not updated for the textures FO4 has. It did add mipmaps for the textures that were supposedly missing some and shrank the resolution; however, seeing as the Creation Kit uses Microsoft's own DDS compression program that adds mipmaps automatically, you're literally just re-adding vanilla textures that have been decompressed and then recompressed with extra loss on the visuals and taking up space. Also, specular maps must be compressed with the Photoshop Intel plugin in order to compress them properly or a program that will allow you to have the red and green channels saved in BC5U format (which is a normal map compression and flipped). GIMP does not do it correctly and I'm very doubtful the program that was used to shrink things did either since it was not designed for FO4's specularity.

DirectXTex

The images are in a split DDS format. To convert them to e.g. PNG files, you first have to concat the files and then use a tool such as texconv.

Yep, the images used for each part of the minigame (a couple variations each of lock background, pick, pins, and springs) are stored as .dds files, DXT1 format. You can convert another image format to this type of texture-- I used texconv. Overwriting the default textures with your new files will replace the assets ingame.

However I've found that MS TexConv from the DirectXTex package is the best way for loosing less quality, so I save my textures as lossless PNGs and use TexConv with my own wrapper then.

You can use texdiag to see information about a texture.

I know only Nvidia texture tools exporter but it's not in masse sorry My suggestion is to create a python script that uses texconv.exe for every file in a directory, pretty easy to get

xLODGen/DynDOLOD/TexGen uses Texoncv to compress textures.

Not necessary on Xbox. Xbox graphics will not function properly without mipmaps so the developers would have had to run everything through xtexconv for Xbox optimization. See Microsoft Documentation on DirectXTex. Code samples for xtexconv for the curious are located here.

All textures/images are .dds files. I use TexConv.exe to convert them to png files. texconv.exe *.dds -ft png

Csv files does not contain formatting so you need to make a proper excel file, which is a whole other beast. Take a look at https://github.com/amiremohamadi/DuckX