That's right. But the unconditioned is the cessation of the conditioned, not the arising of something. But if we speak about anatta, it doesn't matter, because the unconditioned is also anatta. "Sabbe sankhara anicca", means all the conditioned is impermanent, but "sabbe dhamma anatta", means everything is anatta, both conditioned and unconditioned.
It's stated like that, because anicca and dukkha speak about the presence of something, while anatta speaks about the absence of something. Suffering and impermanence are existing things here, but anatta means there is not a self here, so in that sense it is not an existing reality. I hope you understand it like this, because I have difficulty rephrasing. Since the unconditioned is the cessation of things, we can only speak of the absence of things. So, suffering and impermanence cease, but not anatta, because anatta was not an existing thing in the first place. So it's not like anatta is replaced by atta. That's impossible.
If you see it like this, you see why anatta, dukkha and anicca are three terms pointing to the same thing. Three dhamma doors, if you wish. Because of anatta, there is impermanence. Because of impermanence, there is suffering.