Here’s an example of an Executive Order “making law.” The most famous Executive Order in American history was issued by Abraham Lincoln. From the Union’s point of view, it “freed the slaves” in the states in rebellion under the President’s constitutional authority as Commander-in-Chief. From the point of view of the Confederacy, it deprived sovereign citizens of a seperate nation of their lawful property without just compensation.
If the Emancipation Proclamation applied to a “separate nation,” then there would be no constitutional grounds to oppose it.