Likely considered the pinnacle of the Yamanaka clan's techniques, the Mind Body Switch is the jutsu they're most known for. It works on the principle of sending your own mind or conciousness towards the target, and with that done you suppress their own and take a hold of their body. Alternatively, the user can switch the mind of himself with the target, which is another great use in general, but I'll get to that later.
The main purpose of this technique was for supplementary purposes, such as intelligence gathering, reconnaisance and so on, the possibilities of what one can do with this jutsu is pretty unlimited if you asked me. In essence this jutsu has two specific ways of performance: possession, and switching.
Possession works as the initial use, where the Yamanaka will send their conciousness to the target and take a hold of their body. This works by suppressing the target's own conciousness and possessing the body as if it were their own. Naturally, this allows the user to use their body in any way, shape or form they like. This includes but is not limited to their movements, chakra, general shape etc. An instance would be I could take hold of someone, and use powerful techniques just to waste their own chakra reserves. The downside to the chakra means you can only use what the host would know, as it would be physically impossible otherwise. If the target didn't know any Fire ninjutsu, I wouldn't be able to use it while in possession of their body. In short, it requires both parties to be physically capable of using the techniques to use them.
This usage is also used for the supplements of spying, intel and recon. It allows you to take control of helpless people, animals and use their body as if it were your own, unbeknownst to other people that you are the person in possession. It also allows for communication within the mind, allowing for a subtle form of talking to another person.
The biggest downfall of this particular usage is it leaves your body defenseless. In its supplementary use this is a technique best used while hidden, so a person can't do anything damaging to the original body. In a battle there's not much you can do aside from set up some defenses beforehand.
The second application is the switch. It works within the same parameters as the initial use, but with the difference being the target will take possession of your own body in the process. It eliminates the biggest downfall of the first usage, that being the leaving your body as if it were dead aspect. Ideally you would use this on someone allied with you so they can still fight within you; using it on someone hostile towards you may not be the best action you can take, as they can still fight back with your body and chakra. It seems they also have the same reign over your body as you would theirs, with the only difference being they may not be aware of what is happening, and as such would leave an opening to attack. But in this RP no one would actually work that way, so it's a moot point lol.
This is just me theorycrafting, but I feel as if the best application of this jutsu would be to eliminate an ally from a genjutsu where they wouldn't be capable of doing anything. Considering that's an assault on the mind, and this would be casually switching minds, I'm not actually sure what would happen in that case, but I'm guessing you could easily break the illusion through that method. I could be wrong about that, probably something I'd have to ask Kevin about.
As a whole, this technique while extremely powerful seems to have quite a few shortcomings. The first and most glaring being it leaves your body defenseless. In a one-on-one fight this may not be a huge detriment, but in general, or fights with more than one person it wouldn't be a great idea to just outright perform this without taking that into consideration. The second being that this technique travels in a straight line, so while it does have a long range aspect you still have to consider that the possibility of missing is a big problem. Not only that, but missing in general puts your body into the defenseless stasis while you wait for the mind to return to the body. Thirdly, this creates a physical and mental link between the user and their target, meaning any damage the target takes while possessed will be reflected onto the user. I'm not sure if this would work inversely, as in the target taking damage if the original body is hurt, but that's a bridge I'll cross when I get to it.
Looking at the rules of engagement, there's no real difference between how it would work with this jutsu. The only real thing I could mention is that I would believe it only works in accordance to unwilling participants. If someone is willing to become susceptible to the mind transfer, you could consider this without restriction.
Looking at everything I do have a couple of questions. The first being what would be the main perception of this technique being used? From what I can tell it's an invisible projectile so to speak, not to mention it's sending the mind, not chakra. How would you go about knowing that this technique is being used? I'm guessing it'd be your standard chakra sensing, or doujutsu... Secondly could this possibly work through terrain, such as walls, trees etc?
I didn't expect this to be so long, sorry about that!