[PrinzMegaherz]

imho this sounds like a neat idea and it would even add a new "flair" to themes (the first "real" theme that not only changes troops but makes a major change in gameplay)

Mictlan itself has different game mechanics from the rest of the nation (no dominion without blood sacrifice)

Perhaps, instead, it should cause reduced unrest, depending on dominion, as it's a populace belief thing and dominion theoretically reflects the proportion of people in the province who believe in the cause. A reduction to, say, UnrestChange = StandardUnrestChange * min(1,(10-Dominion)/10), would be an advantage inside your own dominion, but would only reduce the unrest increase to 0 where dominion has reached 10.

Thats even better. But you should add that a dominion of 10 could produce free blood slaves without hunting, because the girls offer themselves