As I said before... they don't have mind police. If you converted to Judaism and didn't tell anyone you'd still have made the choice and converted. No-one would know.
I'm guessing you agree you can't change your race? But someone's religion is a choice in their mind, it doesn't need to be a public acknowledgement of what religion you believe is true. So do you think it is impossible for anyone no matter where in the world to change religion?