"Cook the body of a black cat in boiling water with white seeds and wood from the willow until the meat is loosened from the bones. Strain the bones in a linen cloth and, in front of the mirror, place the bones, one by one in your mouth, until you find that you have the magic to make you become invisible. Keep the bone with the magic property and, if you want to go somewhere without being seen, place the bone in your mouth."I can understand completely not wanting to perform this ritual, and do not personally recommend that anyone do so. That being said, I feel that the rite is an essential part of unlocking the power associated with the charm, and that without carrying out the task one does not have a true black cat bone in the grimoire sense. I draw similarities between this ritual and the equally well known Toad bone rite of Witchcraft tradition. In fact some hoodooist believed that one method of finding the bone within the ca that contained power was by throwing the bones in a stream and taking the one that floated upstream. This is the method used in the Toad Bone rite. With the Toad Bone, the process of finding the animal, the method of killing it, the harvesting of the bones, the forces called up during the rite, and the obtaining of the bone are essential. In some ways it is a rite of passage and initiatory in some aspects, I would say that the same holds true for the black cat bone spell in a way as well.
This is not just a simple spell, or mindless killing, It is a rite. One can gleam clues of how some workers viewed this process in the book "Of Mules and Men" where Zora Neale Hurston recounts her own black cat bone ritual, that included a period of fasting before the spiritual undertaking. Periods of fasting usually precede rituals that aim to transform the spirit(s) of those involved in some way. That in my view is part of the aim of the ritual. Lets be honest, this ritual is ghastly and inhumane, which is intended. Mind you it is not as extreme as one of it's predecessors the Taigheirm but I feel it is meant to test the performer on a psychological and thus a spiritual level. Most decent folks would never pointlessly torture an innocent animal, and that is why it tests you. There is a clear line of decency that must be crossed here. Not just one of social convention, or personal moral judgement, but one that you can just recognize on an intuitive level as being "wrong". So then the question that gets asked is, how far are you willing to go for the power that you seek? The process should be hard for you to stomach and get through. If you are a psychopath I just don't think that the rite will have the same deep emotional effect on you.
I am not saying in any way that people should go out and kill a cat if they want an authentic black cat bone charm. I am just saying that we in the conjure community should acknowledge that the ritual served a purpose in empowering the charm, that can't be replaced by any acceptable proxy. One can work black cat magic any way that they see fit, but be honest and know that what you are wielding in no way resembles the legendary charm in my opinion.