The fact that there isn't any body swamping spells is the fact that the only way to achieve such a thing is if one astral projects themselves into the astral plane and there for traveling to so said person and forcing your way into their body, or you can sever the cord that connects your spirit to your body and there for willing your body to basically die, and going off to posse someone.

Possessing some one is harder then one would imagine, the best bet is to find a child(new born children are the best bet) with a weak will, or you can find a teenager whom wishes to die(suicide) and take over. Possessing someone can end up either benefiting the person whom is taking over or kill the person whom is being possessed.

That is why so many demons' whom posses people kill their victims in the process, very few actually survive a possession. If I was you don't do it, you can make your life better by not doing a body swap. Its quite hard to achieve such a thing, and If you do achieve such a thing, you'll be considered a walk-in on from there.

I hope I have helped with this and answered your question

Blessed Be.

always wanted to kno bout this kind of thing

I don't think you will have full control on them until they die. if you kill them their body is yours, and then you can surely control it as you wish because there will be no one to stop you. But I think that since you are clearly not a demon, doing something like that would probably make you of some sort..like a split personality? you will be able to control them when they are weak in mind but if they gather power you will probably get pushed a side. Though are oyu sure you are willing to kill your own body for such a thing? I think this kind of thing could be done only when you lost all hope in your own life and just want to live another life...like wishing to die but not really wanting to so just change your own life. if that is your wish I suggest you to try and do it because you got nothing really to lose if you are wishing to die anyway...
and if it works you can perhaps let us know, that sounds very interesting

If you have given up on hoping for a better life then do so. But I caution you to practice before actually trying to take over someones body and if you do so combine with that person's spirit you wont have control only on those moments of high insurcurity of when the emotions range out of control also, and that person will inherit your memories also the person from there after will have very unstable emotions.

Remember there is a chance you'll never ever be the same after you do this.