Kristin Maloney, prototypical sweet young thing of “Musical of Musical (The Musical!)” at Playhouse in the Park is off-stage till Friday, at least. She was undone last weekend by strained vocal cords. Understudy Margaret-Ellen Jeffreys of the theater’s intern company steps in from “A Christmas Carol,” with a little bit of shuffling around the edges in the holiday classic, which begins student performances tomorrow. Reservations for both shows: 513-421-3888.