Isn't that what an actor does? The good ones at least, change their body language, their voice, their general demeanor. The very best ones, who can actually emulate behavior and make it believable, train, and study, and make it their life's work. They are preparing constantly. And even they fuck it up all the time. They need to do multiple takes, and they need everything around them set up perfectly. They have to do all sorts of things to get in the right headspace.
You shouldn't be trying to force your own body language. If you want to be seen as confident and charming, you need to practice enough in social situations to be relaxed. You don't simply adopt the mannerisms a confident person has. You put yourself through something enough times that you know it in and out and the confidence comes naturally.
If you're trying to use your own body language to subtly manipulate people, you're trying too hard. I mean that both proverbially and literally. Not only does it make you come off awkwardly to anyone paying lots of attention, but it's just not needed. People are fucking easy to manipulate. It's hard not to manipulate people. The older I get the more I see all the ways I've manipulated people, and the was they have manipulated me. And it just makes me sad. Eventually you find yourself in a situation where you wonder if anyone knows the real you.
Look for the people who think you're a good enough friend that they can just be themselves around you, and try to do the same in return.