Are the four characteristics -- production, abiding, change and destruction -- empty, conceptual constructions? Are the four characteristics -- production, abiding, change and destruction -- empty, conceptual constructions? Does this make production etc., perhaps even impermanence, an illusion, especially according to hua-yen Buddhism [as that's where I've seen these four characteristic enumerated]?



I do not think this is a mere "metaphysical" question in the pejorative, because it may say something about birth and death: whether or not samsara -- karmic conditioning -- and so nirvana -- its termination -- are empty of essence; what the nature of first and third noble truths are.
Well, obviously the notions of production etc are dependent on having the notion of a finite, spatially/temporaly/qualitatively bounded entity (phenomenon) that is being produced etc. 

Since the bounds determining the identity of any such entity (phenomenon) are necessarily a product of an act of analysis aka imputation, its production etc. is an empty conceptual construct.

As you correctly supposed, suffering, cessation of suffering, samsara, and cessation of samsara are conceptually constructed notions in the same vein. Hence all the Mahayana talk about transcending the duality of Samsara/Nirvana, liberation from even the concept of liberation, entering true emptiness, the groundless ground etc.