I don't think it is a horror story. If true, it would be a way to deal with the past. I think this is a standard in religion, to walk a way on which you deal with your own past up to a state of completion.
I can see that a dealing with a now unwelcome Christian past is a theme in Wicca, because it is a Western movement. Therefor most practitioners would have a Western past in one way or another.
If it is not too costly for you and you can find something out, I would be thankful. Maybe even only a comparison with other existing Wiccan rituals to deal with the past.
Historically, Gardner was looking at creating a naturalistic Thelema. A lot of whoopie witches glomed onto that and turned it into crystal toting fairies kind of religion.
I know of the Gnostic Mass from Thelema, but again, theres nothing like what you're describing. Similar, with the Golden Dawn, or Theosophy, or Enochian magic - There's nothing like what you describe.
You do say "witches" which I will assume European magical tradition. My first reaction is that what you say is akin to "telephone game" and stories so convoluted that its just a horror story.
I can ask some of my sources whom know more, but this doesn't sound like a credible story.