Yes, I checked it out -- as I do check most leftist claims -- and for once it turns out to be true: By federal law, the John F. Kennedy Center for the Performing Arts is a national memorial, and any change to its name requires an act of Congress.
So unless Trump does get that act of Congress the name change is illegal. Good call on your part; but it still is not an act of stolen valor. It's just and act of tackiness on Trump's part.