TBH this is just pandering for local votes. It has, in reality, no meaning at all. If the feds or the state want to press charges, the county will not stand in the way.
It's ironic too. People think selective enforcement of laws is a good thing. Do you think these counties will not prosecute for firearms violations for people they view disfavorably, e.g. felons, etc.? When you create systems of selective enforcement of laws, the end result is a system where law enforcement can, and will selectively abuse it. Not only that, any shield against enforcement is passing in the wind, and a political weapon; a "resolution" means jack squat, and at any moment they can decide to arrest and prosecute. Better hope you don't piss the "wrong" people off at that point.