Stimbo, I'm pretty sure there are lots of girls who would go for nice guys instead of bad-ass guys.
Either way, I really don't think you have to re-invent yourself in such an extreme way by becoming a "bad-ass" all of a sudden just for the purpose of finding a girl. If you do that, then you're not being honest with yourself and others, and it can possibly lead to worse consequences for you in the future. I don't think anything good will come out of that.
As others have said, simply be who you are, not what someone else expects you to be.
Either way, I really don't think you have to re-invent yourself in such an extreme way by becoming a "bad-ass" all of a sudden just for the purpose of finding a girl. If you do that, then you're not being honest with yourself and others, and it can possibly lead to worse consequences for you in the future. I don't think anything good will come out of that.
As others have said, simply be who you are, not what someone else expects you to be.