Retrograde planets will not do harm in native charts. In horary charts, the retrograde planets will give their results after their motion becomes direct.
KP astrology is not separate to Traditional astrology. Walking God Kanchi Paramacharya blessed Acharya KSK to fill the gaps. With their kind blessings, Sri KSK could get the blessings of Uchchista Ganapathi and propounded this theory. The readings are as per Parasara Sastra only.
Thank you for having a good opinion about this theory.