Again, you are missing my point. I'll make this as simple as possible.
You walk into a bar, you see a guy in the corner, in the dark, with an angry expression on his face, holding a knife. He looks like bad news, so you avoid him. Is he actually a bad guy? Maybe not, maybe he's having a rough day and his knife fell out of his pocket just before you walked in. If he puts his knife away, and changes his facial expression, does that make him a different person? No, it doesn't. But do you know what it does accomplish? It makes him more approachable. Now let's apply this to you. You have a grumpy look on your face, you're slouching, you've got ketchup on your shirt because you had a nice burger earlier. Does this make you a bad guy? No. Will girls talk to you? Probably not.(this is all example, please don't take this literally, I'm not saying you walk around with ketchup on your shirt but somehow I think you might)
It's not about changing who you are, it's about making yourself seem available. If you present yourself as too aggressive or too timid, some people won't always give you a chance even if they would like you just the way you are.
Don't change who you are, change how you tell people who you are. Not everyone speaks your metaphorical language, so you need to adjust.
Again, let me reiterate, it's not changing who you are, your core substance, or even to an extent the facade you wear. Just be aware the effect you have on first impressions, and if your first impression doesn't represent who you are, maybe tweak it a little.
Because if you honestly believe the kind of person you are should be able to establish relationships or even if you just want to get laid and it's not happening, perhaps people are getting the wrong read off of you.
It takes work, I'm not saying it doesn't. But you can do this without changing your person. You may need to come to terms that you're expecting too much of the world.