Well, if it were to be done, this would be the place.
As far as I know, you can't "import" things into the game yet--like, you can't go and create Cloud's AC Buster Sword in some program, and then input it into the game. As of yet, there just isn't any method for doing it. You can expect it, though, in the near future, most likely.
The closest thing I think you could do is modify the current Buster Sword to your tastes...how to do that, though, I'm not sure. Someone a bit more knowledgable in that area may be able to tell you, though.