Reeve Carney, lead thesp in Broadway tuner “Spider-Man: Turn Off the Dark,” has extended his contract with the production and will stay with the show through May.Move means Carney, who plays Peter Parker in the comicbook musical, will be with the musical (which began previews in late November) for about 18 months. Although “Spider-Man” is far from star-driven, thesp nonetheless emerged prominently over the course of the media frenzy surrounding the show’s long, rocky road to opening night. This winter, however, Carney will temporarily exit “Spider-Man” to play the protag in an untitled Jeff Buckley biopic, one of two films currently in the works about the late cult-fave musician. “Spider-Man” has spent the summer logging weekly sales of more than $1 million per week, regularly landing on the higher end of the top 10. Show’s $1.2 million tally from last week — when most of Broadway plummeted in the back-to-school slowdown — could indicate the tuner has attracted enough enduring interest to keep sales high even during traditionally fallow frames. While Carney’s out of “Spider-Man,” his role will be played by Matthew James Thomas, already Carney’s alternate for two shows a week, and Matt Caplan. It’s not yet clear how long other cast members, including Jennifer Damiano and Patrick Page, intend to remain with the show.