The problem is not so much that the US Postal Service gives these favorable rates to China, so much as the UPU (Universal Postal Union) decrees it. We are a member of the UPU and it heavily (like every other damn international organization) relies on the US to cover the rest of the world with subsidies.
So? He who eats my bread sings my song.
An EO freezing payments to UPU ‘until Chyna is recognized as a world power no longer eligible for a free ride’ would do what to the UPU’s ‘tude?