@clacke So, for people who just wanna to being atheist or agnostic, de jure, they must stated what their religion on their ID card. But de facto, they can do whatever they want, without being tied or practising with the religion law/norm they stated on their ID card, as long as whatever they did isn't break or violating with the general legal law.
Non-religion behavior such as atheist or agnostic, are not legally recognised, as its incompatible with Pancasila.