This is for the Dunmer traditions and from the Vivec sermons if not mistaken so it shoudl show something like reaching an illumination and path top heaven or santitude not really becoming a God ... no?
The principle works in general. You might say that Vivec has some expert knowledge.
Perhaps a parallel would help.
James Bond. When I say that name, are you thinking of Sean Connery, Roger Moore, Timothy Dalton, Pierce Brosnan, or Daniel Craig? They've all been acting the part and many people think of one specific actor as the real James Bond.
Now imagine a world where such thought matter. Imagine a world were acting like something makes you that thing in other aspects. It's basic magical thinking really, think https://en.wikipedia.org/wiki/Cargo_cult.
The how and why are not so easy to explain, that understanding comes from trying to make sense of it all but let's presume the world works that way.
Now if you do this, act like James Bond, you become indistinguishable from James Bond, if you do it long enough people, or rather the world, will expect James Bond to behave like you. At this point you've become James Bond and it is no longer an act.
Manteling works in the same fashion.
Now you've mentioned Zurin Arctus a few time but he's not quite that relevant to Tiber manteling Ysmir. Rather he's part of a recurrent mythic story, a story that resembles a larger story and thus gives it's participants the same significance as the original actors in this story. The actors in this story are called the Enantiomorph and are typically reflections of Lorkhan and Akatosh. Or at a cosmic scale Anu and Padomay. There is also a small supporting cast, a love interest, a witness struck blind and a few others I can't recall.