WARNING: POTENTIAL MEMETIC HAZARD

I've kinda been avoiding this due to the potential correlation between my magickal experimentation in my teens/twenties and my later-life mental health difficulties, but I feel like people are wandering all over the place already, and I'd at least like to provide a few guideposts.

Yes, there are processes. Or at least, there are various things that are roughly like processes, although very few of them are formalized (if you want formalization, look to Crowley). Rather than provide yet another anecdotal account, let me lay out some of the observations I made during my own experimentation. My explicit goal when experimenting was to attempt to map various wacky "occult" or "pseudoscientific" theories to a modern understanding of neuroscience, and thus explain away as much of the Woo as possible. My hope was that what was left would provide a reasonable guide to "hacking my wetware".

1. When you're doing occult procedures, what (I think, @p > 0.7) you're essentially doing is performing code injection attacks on your own brain. Note that while the brain is a neural network rather than a serial von Neumann-type (or Turing-type) machine, many neural networks tend to converge towards emulating finite state machines, which can be modeled as von Neumann-type machines - so it's not implausible (@p ~= 0.85) that processes analagous to code injection attacks might work.

2. The specific area of the brain that seems to be targeted by the rituals that create a tulpa are the right inferior parietal lobe and the temporoparietal junction - which seem to play a key role in maintaining one's sense-of-self / sense-of-agency / sense-of-ownership (i.e., the illusion that there is an "I" and that that "I" is what is calling the shots when the mind makes a decision or the body performs an action), as well as the area of the inferior parietal cortex and postcentral gyrus that participate in so-called "mirror neuron" processes. You'll note that Crowley, for example, goes through at great length describing rather brutal initiatory ordeals designed specifically to degrade the practitioner's sense-of-self - Crowley's specific method was tabooing the word 'I', and slashing his own thumb with a razor whenever he slipped.

3. NOTE: Tabooing "I" is a VERY POWERFUL technique, and unlocks a slew of potential mindhacks, but (to stretch our software metaphor to the breaking point) you're basically crashing one of your more important pieces of firewall software so you can do it. ARE YOU SURE THAT'S WHAT YOU WANT TO BE DOING? You literally have no idea how many little things constantly assault the ego / sense of self-worth every minute that you don't even register because your "I" protects you. A good deal of Crowley's (or any good initiatory Master's) training involves preparing you to protect yourself once you take that firewall down - older works will couch that as "warding you against evil spirits" or whatever, but ultimately what we're talking about is the terrifying and relentless psychological onslaught that is raw, unfiltered reality (or, to be more accurate, "rawer, less-filtered reality").

3A) ARE YOU SURE THAT IS WHAT YOU WANT TO DO TO YOUR BRAIN?

1. Once your "I" crashes, you can start your injection attacks. Basically, while the "I" is rebooting, you want to slip stuff into your sensory stream that will disrupt the rebooting process enough to spawn two seperate "I" processes - essentially, you need to confuse your brain into thinking that it needs to spawn a second "I" while the first one is still running, confuse each "I" into not noticing that the other one is actually running on the same hardware, and then load a bunch of bogus metadata into one of the "I"s so that it develops a separate personality and set of motivations.

2. Luckily, this is easier than it sounds, because your brain is already used to doing exactly this up in the prefrontal cortex - this is the origin of all that BS "right brain" / "left brain" talk that came from those fascinating epilepsy studies where they severed people's corpus colossa. See, you actually have two separate "awareness" processes running already; it's just that your corpus colossum normally keeps them sufficiently synchronized that you don't notice, and you only have a single "I" providing a consistent narrative, so you never notice that you're actually two separate conscious processes cooperating and competing for goal-satisfaction.

Anyway, hopefully this has been informative enough that dedicated psychonauts can use it as a launching point, while obfuscated enough that people won't be casually frying their brains. This ain't rocket science yet.

Fair point. OK, the fact that it's reversible seems about as agreed on as any facet of this topic - more so than many of them. I'm inclined to believe this isn't a hoax or anything due to the sheer number of people claiming to have done it and (apparent?) lack of failed replications. None of this is accepted science or anything, there is a certain degree of risk from Side Effects No-one Saw Coming and hey, maybe it's magic and your soul will get nommed (although most online proponents are careful to disavow claims that it's anything but an induced hallucination.)

They ought to be at least somewhat concerned that they have less brain for their own walking around the house.

Ah, right. I suppose that would depend on the exact mechanisms, involved, yeah.

Are children who have imaginary friends found to have subnormal cognitive development?

You don't know? It's loss in "utility". When you have an unknown item which, out of the items that you know of, most closely resembles a mushroom consumption of which had very huge negative utility, the expected utility of consuming the unknown toxic mushroom like item is also negative (unless totally starving and there's literally nothing else one could seek for nourishment).

So please provide evidence that this feature is shared by the thing under discussion, yeah?

The cases I've heard which do not look like people attention seeking online, are associated with severe mental illness.

Source? This doesn't match my experiences, unless you draw an extremely wide definition of "attention-seeking online" (I assume you meant to imply people who were probably making it up?)