2 questions on blood sacrifice

[tinkthank]

After perusing the older threads on this subject and having read the excellent dominion spread guide (whose link I no longer have...), I have these questions:

1. In order for a person to sacrifice, he must be in a province with a temple and must have at least 1 blood slave in his personal gem box. If you try to give him or her the command without those slaves, the warning message appears. After having sacrificed on the subsequent turn, that person will have less slaves in his or her possession, possibly zero (depending on how many s/he had been given). I would like to consider the scenario where s/he has none remaining.
Now if you do not change orders for that person (that is: the command "perform blood sacrifice" stays up), you will receive no error message. My question is: is this similar to what happens when you set a, say, level 2 priest to "preach" in a province with a temple and then forget about him? That is: At some point, your dominion hits 4 or more, but the priest will keep preaching; if you manually order him to preach, you will get the warning message.
I would like to rephrase the question: Apparently, if you order your Blood Sacrificer to sacrifice when in a province *with a lab*, s/he will automatically suck out more slaves from the lab. This is what has been said in other Posts. But I am unsure. You will see his or her gem slots still be empty, and there is no real way to see if dominion rises due to sacrifice or due to a normal temple check. How many slaves are replaced, if any, when
So is there anyway to find out how "replacing blood slaves" / performing blood sacrifices over multiple turns really works?
Thanks much

2. Can someone tell me if I have understood this correctly? Blood sacrifice works much like extra, manually induced temple checks. That is, the blood sacrificer performing the ritual will induce 1 extra temple check per blood slave sacrificed. And *that* means: Unlike preaching, this can affect dominion spread even when the dominion is higher than that priest's level. And *that* means: blood sacrifice *can* make sense *even* when dominion has reached its maximum (10) in a province (for example: when the neighboring provinces are under 10) by affecting its neighbors, although there may be more meaningful things to do with those slaves, but whatever. Am I right so far? Now if the neighboring provinces of a temple are also all 10, will the temple check spread then spread to *those* neighbors (much like I feel that the home capital spreads dominion)? Thanks in advance