If anyone can make a 19th-century opera relevant to young 21st-century audiences, you can bet it’s Baz Luhrmann. The Australian director behind Moulin Rouge, is using many of the same pyrotechnics and storytelling techniques of that movie in his new Broadway production of Puccini’s La Boheme. But Luhrmann insists that, despite the updated look of the show, he is against modernizing a classic operatic plot just to “be groovy.”