If the universe was fine tuned for our life...

[robvalue]

It seems like you're only defining "rules" in an abstract way here. If I make a mine craft level or something, no rules of the universe are changing in that. A computer and screen follow your regular rules. Only if you abstractly view the new "world" in its own right can you describe new rules, but that is not descriptive of the reality of the situation.

I really don't get what a sub reality is supposed to be. The only definition I could think of that makes any sense is an entirely closed system within a reality, so that it occupies physical space in the reality but is cut off at some sort of boundary through which nothing can pass.

But even then, if you could make such a thing (I don't know if it will ever be possible) you are extrapolating to try and deduce something about our universe. We don't know if our universe is open or closed, infinite or finite, is within another universe or parallel to others or whatever. You can't just observe internal rules and assume they apply to the universe itself. Well you can, but you'd almost certainly be wrong.

"The outsides of all the objects in my house are blue" does not imply "The outside of my house is blue".