Things got a little personal at the opening- night party for Broadway tuner “How to Succeed in Business Without Really Trying” Sunday at the Plaza.Lead Daniel Radcliffe confided that he imagined he’d be terrified every night prior to his big dance moment in song “Brotherhood of Man.” But it turns out it’s been fun. “No matter how good or bad for me personally a show has gone, I know with that number, all is forgiven,” he said. Also sharing was cast member Christopher J. Hanke, who cracked: “I change my underwear twice during the show, because they’re that sweaty.” For Neil Meron, who produces with Craig Zadan and Broadway Across America(led by John Gore, Thomas B. McGrath and Beth Williams), “How to Succeed” holds a special place in his heart. “The original production was the first Broadway show I ever saw,” he said. Co-star Rose Hemingway also has a past with the show: In high school, she was an understudy in the chorus role of pirate dancer. “You gotta start somewhere,” she said. Indeed.