Hi there!
Nope, not at all impossible. Bfb and materials are a new thing that was added in ES to help improve graphics without slowing down machines. So first off, if you are looking in ES files and finding the bfb and materials, check the original game files and there you should find the .nif and the icon.dds file. (a few objects and all mm stuff don't have nif files at all, but very few. If this happens, don't panic, you just have to code it like you would if there was a .nif file).
Now, I think I sent instructions on editing them.. let me see if I can find it. Yup! here it is :
So the .bfb file should be renamed to the same as the .nif file. It corresponds to a .nif file and is rarely seen without one. You open them the same way you open the .nif file. Now inside of it, there will be text that matches each of the materials files that it needs. They may appear more than once so I recomended finding a text in each of them and just replacing that, as always, don't change the number of letters.
Now rename the materials files to match and then open them in notepad. Inside most there will be a
section which will have a dds name. Just change that to yours and you are done!
So, you'll want to edit the .nif as well. Now if you're having trouble finding skins, I can give you some pointers, but it can be tricky. If you are making an object that was in original zt, most likely it will be in entities/objects/shared, but sometimes it will be in simple shared.z2f or it will be in like entities/objects/scenery/shared. If you are making one from an xp, they are almost always in the xp files and just in shared. Does this make sense? If you know of a specific skin you need I can look for it too
Best of luck and just ask if you need anything else. (and sorry for such a long post lol)