Personally, I think there's about a 90% chance the story is totally fake. CNN doesn't name names, and there's no confirmation from Cohen or his lawyer.
But... if Cohen does indeed plan to change his prior sworn testimony and now claim he and Trump knew of the meeting in advance, I still fail to see the significance... other than Don Jr. having sworn to the contrary. Perhaps the plan is to indict Don Jr. for perjury in hopes Trump will give up or something.