snip from the article>

The Church Protection Act does more than allow churches to create security programs to train parishioners to carry concealed weapons, and set up armed security forces for the protection of congregations.

It also allows Mississippians to carry guns in holsters without a permit and prohibits state officials from enforcing any federal agency regulations or executive orders that would violate the Mississippi Constitution.

Sen. Hob Bryan (D) thought that was a clear violation of the Supremacy Clause of the U.S. Constitution that guarantees federal law always trumps state law.

snip> more at link

State actors are not required to enforce federal regulations.

the Washington and Colorado pot laws are too. No it doesn't violate the Supremacy Clause, has nothing to do with it. Local officials are often not authorized to enforce federal law. My understanding is that local officials have to be specifically authorized to enforce those laws.
I would argue, and I do, that the law this repealed violated the separation of Church and State.

Does it really say church security personnel have the authority to "shoot to kill"? Do they only have this authority in church or does it extend outside churches? Do you need to be a licensed "soldier of God" to be above the law?

Puhleeze.