"The Act permits the President to grant a one-time extension of no more than 90 days with respect to the prohibitions’ 270-day effective date if the President makes certain certifications to Congress regarding progress toward a qualified divestiture."

Sounds like he needs to work with Congress on at least a basic level for this to be within the law, not just make his own decision and declare all is good. And there is the small detail that he is not President, at least not today.