I don't think Yoruichi's cat transformation ability is ever explained. From what I have seen, it is a unique ability in the Bleach universe. Perhaps it's a unique innate trait, like Zaraki's ability to endure/ignore pain.

I'm not terribly picky about changes between subbed/dubbed anime, but I just watched the latest dubbed ep on Adult Swim, and I rather dislike what they've done with Byakuya's voice. Rather than his original dignified indoor-voice, he now has a baritone yell-talk.