Detailed information and install instructions can be found on MyAnimeList.
Feel free to modify any of these themes as much as you want and use them however you want. That said, if you are using any of my designs I do ask that you leave the sign off I place in the footers of my designs intact or replace it with an equally findable piece of information stating that I made the theme. At the end of the day, however, the only thing I care about is that you don't claim you made it.
On a different note, I do not care if you take pieces of my code, modify it and mash it together with other code to create something new. That is the nature of things and I am perfectly fine with it. Go right ahead and create a frankenstein list design, as long as it is sufficiently transformative I do not wish for any credit.