Jeff Goldblum will take over the lead role in Broadway play “Seminar” in April, when current topliner Alan Rickman exits the production.Goldblum, last on the Rialto in “The Pillowman” in 2005, has skedded an eight-week run in the show, which opened in November to generally strong reviews and solid, if not stellar, box office. It’s not yet clear who, if any, of Rickman’s four current co-stars — Lily Rabe, Hamish Linklater, Jerry O’Connell and Hettienne Park — will stay on with the production when Rickman departs. Play by Theresa Rebeck (“Smash”) centers on a cocky literary giant teaching a private class to aspiring young writers. Production, a world preem that opened cold on the Main Stem, is produced by Jeffrey Finn, Jill Furman, John N. Hart Jr., Patrick Milling Smith, Roy Furman, David Ian, David Mirvish, Amy Nauiokas and James Spry. Rickman ends his run in “Seminar” April 1, with Goldblum stepping into the part starting April 3.