Although the lesser magistrate has the right to enforce good even if the greater magistrate forbids it, it does not follow that the lesser magistrate must under all circumstances enforce the good. Consider Larger Catechism Question 99.5 "That what God forbids, is at no time to be done; what he commands, is always our duty; [430] and yet every particular duty is not to be done at all times."
To your particular scenario, it does not match up with your implicit question that I attempted to answer above. I think you would want the scenario to be that the lesser magistrate be
willing to attempt to stop murder from occurring at the clinics (not that a citizen asks as such). The magistrate (or anyone for that matter) is forbidden from murder. And the magistrate is commanded to stop murderers. But that which is commanded is not to be done at all times.
Then the question becomes: under what circumstances should these particular commands (stopping murderers) be accomplished? The Western theory of resistance by the lesser magistrate is under the broader theory of the right of war and resistance to tyrants. And those broader theories always take into consideration the cost of going to war or resisting tyrants. War and violent resistance are always the last option. And more often than not, as the likes of Calvin and other past leaders indicate, it is preferable to live under tyranny than trade it for chaos (if there is only such a choice).
Just some general considerations (see,
here for a Sunday school series on the broader topic).