Here's the thing. You appear to be asking about a specific religion, but there are many groups which call themselves Kemetiic, varying widely in their beliefs and motivations. If you can provide us with the name of an organization from which you / they got the term "Kemetism" to describe some set of beliefs, it would be helpful.
Unless, of course, you are referring to any and all Egyptian revivals or alleged descendants. In that case, here is my general opinion: Ancient Egypt rose, lived and died. We know only a very little bit about it because (last I heard) less than 1% of Ancient Egyptian sites have been discovered / excavated. What's more, the civilization lasted thousands of years, worshiping differently at different times and in different parts of the countrie(s). Then, to confuse things further, random elements of Ancient Egyptian culture, theology, and magic were borrowed into other cultures that still survive today in altered forms which may contradict the original beliefs.
So what makes something "Kemetic?" I would argue that the golden standard of Egyptian-ness is that which is the most original, and therefore that the only true forms of "Kemetism" are those which adhere most closely to primary sources of Egyptian culture. I believe this to be self-evident. Then, if you are inclined to believe in magic, you should appreciate the power that has been invested into the specific symbols used by Egyptians as they originally understood them. Spiritual paradigms that last and develop for thousands of years sustain immensely powerful beings and effective metaphysical arts. Systems like the Egyptian one which knowingly and explicitly used magic and which were extremely ritualistic, even more so.
Given this, one's proximity to original ritual and symbolic understanding determines one's rapport with these beings and forces, so why would an allegedly "Kemetic" organization make things more difficult for practitioners by cluttering its system with foreign metaphysics just to fill gaps? If you think your gods are worth worshiping, learn everything you can and worship them. They can tell you the rest.
This is the safe way - in my opinion. If you start bringing other paradigms into your practice, you risk several things, magically speaking: 1) not connecting to anything; 2) co-utilizing conflicting forces or symbols; and 3) ultimately detracting from the power and integrity of the original spiritual structure that built up over millenia.
As someone who uses theology to structure my symbols in magic and is most drawn to Egyptian forms, I recognize that it is difficult to resist filling in knowledge gaps with other systems. Sometimes, I agree that it is unreasonable not to supplement with other philosophies for practical purposes, and do so myself. However, I believe that it is important that I recognize where I am supplementing, and ensure that that supplementation is legitimate and effective in its own right for my purposes. If, for instance, I thought that "siddhi" and "samadhi" were Egyptian words, and didn't know their actual meanings, this would be a problem, because then I would obviously have no reliable knowledge of either paradigm.
As far as people claiming to be rightful Pharaohs and High Priest(esse)s with the authority to arbitrate Egyptian beliefs, I have been unconvinced so far.
I hope that this was helpful, but please let me know if I was unclear about anything.