George Hearn will replace Joel Grey as the Wizard in “Wicked.”Grey is on an extended leave of absence and has been out of the Broadway musical since mid-June. He was a presenter on the June 6 telecast of the Tony Awards and recently reupped his contract to continue in the musical through the end of 2004. Sean McCourt has played the Wizard in Grey’s absence. Hearn goes into the Oz tuner on July 20, a date that also brings the debuts of two other performers in the “Wizard of Oz” saga. New cast members include Jennifer Laura Thompson as Glinda, replacing Kristin Chenoweth, and Joey McIntyre as Fiyero, replacing Norman Leo Butz. As a performer, Hearn won Tony Awards for his turns in “La Cage aux Folles” (1984) and “Sunset Boulevard” (1995).