I don't really know what restrictions you are talking about. Bringing your own "Mac" and "IPhone" will not be a problem; they've even done away with custom declaration forms.

If you intend to bring numerous of them or sell your personal "Mac" in China without paying duty, you're smuggling - but that would be the same in just about any country in the world. I would not recommend doing this anywhere in the world, including China. Getting caught will mean trouble, heavy fines, and probably imprisonment at some point - anywhere in the world.

Edit: Just to clarify: To import means bringing merchandise from one country into another and leaving it there. When you bring your "Mac" to China to use it and take it back out of the country with you, you are not importing it and do not need to pay duty. After reading your post several times, I take it you just want to do this, right?