I haven't seen too many who were. I guess most fighters fight the way that brought them success and find it difficult to change. Julio Cesar Chavez usually fought one way-straight ahead-but in the Whitaker fight, after realising his usual pressure tactics weren't paying off, he changed tack and backed off, attempting to lure Whitaker in and counter him. It didn't work cause Pernell was too wise for that, but it did show Chavez' versatiliy and his ability to change things up if plan A didn't work. But it's all too rare a quality in most fighers.