I think the whole fake BXJF was to distract and perhaps even hurt ZLC for practicing without castration was very dangerous. Even if it did not hurt ZLC it would waste his time practicing an inferior skill rather than concentrating on his own martial arts.
As for why YBQ did not just speed up his Huashan skills, this could be a reflection of YBQ's limitations. He is someone who fights how he is taught and lacks creativity. It just never occurred to him to do something so inventive.