You're your own worst enemy, as they say. It sounds like it's self-consciousness holding you back, or maybe 'self-awareness' is a better word to use.
I think there are two things worth remembering in this situation. Firstly, only very few people tend to know us as we really and genuinely are, so your concern that people might judge you as fake is for the most part non-existent. People are consistently changing, particularly young people, so it's hardly the most outlandish thing. Honestly, yes, people at school might initially notice that you've made what is in their eyes a 'drastic change' but that's the social climate for you. It's very focused on image. You've already said that you don't want to change your moral fibre and its nuances, so those closest to you will understand that you're not simply taking on a new appearance.
Secondly, and most importantly, you sincerely want to change - so this stereotype that you want to emulate
is you. What I'm trying to say is that you are the person that you are now why? Because life's molded you that way. Now that you're in a position to change, now that you're aware of your choices and the possibilities of expression, do you want to remain the same? No. And it's that choice that is important and that defines you as a person.
You say that you're a part of a drama class and you've participated in a few plays. Would you be able to employ the techniques you use in drama to ease you in to accepting your new 'character' as yourself?
I know it's easier said than done, but it would probably help if you didn't focus on reviving your reputation, and instead saw this change as making a brand new one. This is a ridiculous example, but do you remember
Avril Lavigne's image when she first came into public light? [solarnavigator.net] She was tomboyish, a poster-girl for stores like Claire's Accessories.
And then she changed [images.newcelebritypics.com], and I remember it being a very sudden change. I got the impression that it wasn't a publicity stunt for her to appeal to markets outside of skateboarders and preteen acoustic guitar players, but just something that she'd wanted to do.
I agree with you: courage is key. And confidence, although they're similar things. If conforming to this stereotype is something that you want to do and have wanted to do for a while, I think it'll come across. You might not have the precise mechanics of the lifestyle down but hey, how could you? You haven't been there and done that yet.