Yes, you can switch preferences once you finish signing up.
The "stuck-in-the-signup-loop" thing is also something we're working on. It's a balance between increasing conversions and pissing some people off. We're probably going to switch to a version where you aren't stuck, though, but today we just went with the MVP :)
Fair enough, but IMHO not letting me access the FAQ (which I can access by logging out anyway) won't help you increase conversions. Having a back button to go to the preferences also wouldn't hurt, but that can be debated. At the very least, stating prominently on the sign up page that users will be able to switch preferences after signing up seems like a no brainer.
I respect the idea of shipping the MVP though, and Carwoo looks like a very useful service!
The "stuck-in-the-signup-loop" thing is also something we're working on. It's a balance between increasing conversions and pissing some people off. We're probably going to switch to a version where you aren't stuck, though, but today we just went with the MVP :)