Interesting question. If we can't (be who we really are) after making our exit, what was the point of leaving? We certainly can change and "become" the kind of person we want to be. It just takes some work. I believe anyone who "does the work" to exit the dub life - and by that I mean someone who makes a conscientious decision to leave as opposed to one who just stops going to meetings but doesn't change the dub mindset - can succeed.
The "work" that's involved requires coming to grips with why you were a dub (became one or remained one) in the first place and why you want to leave. It's similar to recovery from an addiction to alcohol or drugs; you have to shed that dependence (in this case on religion) and learn new behavior. All of this requires honest self-examination and a willingness to act on what you discover.