I've been described as charismatic by many people and I have moderate to severe stutter. I don't believe I am innately charismatic though. I rely on "fake it till you make it" mentality. I have also participated in theater, amateur films and always make a big fiasco when I have a presentation. I feel speech is just one aspect of what people see. I like to focus on the other aspects. Tone, speed, props, body language (not stuttering gestures though). Even sometimes nonverbal actions carry out your personality (the other day, I invited everyone at work to pizza on my last day working with them). Also, you said in your post that you substitute words and rearrange sentences, one of the first things I was taught going to speech therapy was to never do that. Better they know I'm a stutterer than think I'm bad at grammar. Let your voice boom with confidence with your stutter. My advice is stutter with confidence and your stutter will slowly improve with that built up confidence. If your confidence takes a hit (someone makes fun of you, someone ignores you, etc.) take it like a champ and hold your head up high, even if you have to fake it. It will come naturally the more you do it. Speak up for yourself, tell them unapologetically that you stutter and say what's on your mind. That's what will stick in most people's minds, not the stutter but the message and the character behind it. Hope this helps.