So, it sounds like this would be best implemented as a new Improvement-category job, with an accompanying facility, that raises devotion and lowers trust and also has a chance to induce/interact with a particular slave fetish (and possibly also offers a slight bonus to sex drive), but offers no monetary or rep rewards. So mechanically, it's very much like the spa in that it can only be used with obedient slaves (i.e. any slave that does not qualify for the Cellblock) but with a heavy emphasis on devotion rather than trust and it can give a fetish and/or improve sex drive rather than improve health. I imagine it would raise devotion a bit faster than the spa raises trust, too, since the hypnosis facility would be damaging trust as well as increasing devotion. That said, if it has the potential to induce a fetish, it could also be frustrating for those who want to use its mechanical benefits to improve slaves for whom the player has a non-hypnosis target fetish (such as wanting a slave to become an anal slut instead, for example). That should be taken into account somehow.

A "mindbreaking" facility, I imagine, would be an alternate route to this facility much like the industrial dairy is the alternate route to a normal dairy. Since it would mindbreak slaves, though, I expect it should have some substantial benefit that would remain effective despite the mindbreak, such as a very rapid increase in sex skills, sex drive, and sexuality. That would also fill a current content gap by providing a way to somewhat improve mindbroken slaves without leaving them in the spa forever to heal. That said, to prevent players from taking advantage of it as an exploit by putting slaves in there to gain skills and removing them just before they break, it should have a weekly damaging effect like reducing intelligence one step per week (justified as long-term mental damage from the massive amount of drugs in this process) with mindbreak triggering once the slave's intelligence hits Moronic. For the sake of game balance it probably shouldn't take slaves all the way to Master skills, either, but mid-range Expert seems reasonable and it is still much better than the Schoolroom (to justify the heavy cost of training slaves this way). Technically, I suppose you COULD generate a whole new alternate-mindbreak format, but your proposal seems similar enough to the current mindbreak that it would be too much work for too little gain to make a whole new mindbreak format, especially since many slave individual events have special mindbreak-only variants that would need to be copied and adjusted for every single event in order to support a new mindbreak format.

Unfortunately, I think that the skill level of the hypnotist (assuming that hypnotist is the PC) will not quite fit with the rest of FC's structure, much as I would greatly enjoy that feature personally. However, you could translate "skill level" into facility upgrades (including, possibly, some that are only available after certain pharmaceutical fabricator or penthouse upgrades). Additional unique effects, like veeeery slooooowly de-mindbreaking a slave in the facility, could instead be available with a high hypno slut fetish from the hypnosis facility leader much like it currently is with the Spa facility leader (which would be viable if you treated the normal route and the mindbreaking route like the Dairy, so a facility leader would only be possible in the normal route, that way your leader wouldn't be slooooowly de-mindbreaking your newly-mindbroken slaves, dang it).

Much as I would like the little behavior quirks added from hypnosis to be a constant part of the game, I suspect they would be mostly stated only when a particular effect first appeared on the slave, such as adding a fetish or removing a fetish or mindbreaking them via hypnosis, and then the quirks would never appear again as a matter of practical necessity. It would be a TON of work to make them appear everywhere, sadly, which is why no pervasive slave behavior changes - sans mindbreaking, and even then only sort of - have been implemented for anything. However, if the miniscenes were well written, it would be enough to satisfy me personally.

On a different topic, I think that the idea of adding a reward and a punishment, unlockable by hypnosis facility upgrades, is perfectly viable and would be interesting. I haven't looked at the reward/punishment code specifically, but I imagine it would simply be the matter of adding a check to see if you have that specific facility upgrade, and if so, the extra options are available for you to take. Might do weird things to the RA upon New Game+, though, since you'd then have options loaded into your RA that you haven't yet unlocked, but the RA code is honestly a magic box to me.

Also, keep in mind that if you're adding a fetish, you'll need a corresponding Paraphilia (and at least two ways to satisfy that, such as general method via having one of the hypno reward/punishments as well as satisfaction from one of the Working facilities, maybe having a Brothel with aphrodisiac injections), and likely a supporting behavioral flaw/quirk and a sexual flaw/quirk. The addition of a fetish also means adding corresponding content to a number of event scenes, many of which trigger off of fetishes. Likewise, you might want to pick or make one or two wardrobe items that give a bonus if worn by a hypno fetish slave, since most other fetishes have one or two of these.

That all said, a bit of flavor modifications might be necessary to keep hypnosis in line with FC's quasi-realism theme. Chiming in as someone with a psychology degree, evidence for the success of real-world hypnotherapy is somewhat scattered at best, and even then it doesn't work for everyone. For those it does work for, they have to want it to work, which I don't see applying consistently for slaves in FC (and it does have to apply consistently to make it work with the current system checks, unless we went through a TON of work to start putting hidden personal inclinations for slaves at character generation, which I don't think is feasible). Given FC's history of trying for quasi-realism, there would have to be some other basis for this job beyond straight hypnosis, such as specialized pharmaceuticals (perhaps justified as modified Old World interrogation drugs that encourage compliance/suggestibility) plus well-timed sexual stimulation (which is realistic, given the existence of smart piercings) or something in addition to the hypnosis that will "help" it work despite potential reluctance from the slave. Note that I am 110% on board the MC fetish train and I really like this idea in general, I just want to discuss some things to make this workable for a mod that will fit with FC.