Since I'm back to basics and all....
To change a texture for an FX, would I use just any hex editor, or should I be looking for a specific one? I don't seem to have one in my backups, so I'm guessing it wasn't anything special.
If you really want to use a Hex Editor, I started using "Frhed" a while back. It was the first one I downloaded, and it seems pretty simple.
http://frhed.sourceforge.net/en/
However, for the purpose of making a new FX and changing the Texture, NifSkope really is 100 times easier. There's a basic Tutorial at the Litterbox for making an FX with NifSkope, it's long, but only because it's detailed and has a lot of pictures. I would definitely suggest trying that one out.