WASHINGTON — Signature Theater in Arlington, Va., has completed principal casting for the U.S. preem in July of “The Witches of Eastwick,” the Cameron Mackintosh musical directed in its 2000 London premiere by Signature a.d. Eric Schaeffer.Emily Skinner, Jacquelyn Piro Donovan and Christiane Noll have been cast as the three witches, while Marc Kudisch will play devilish seducer Darryll Van Horne. Schaeffer says he has significantly reworked the production, which initially played at London’s Drury Lane and Prince of Wales theaters. Show has since been produced in Russia, Japan and Australia. “Eastwick” is based on the John Updike novel and Warner Bros. film, with book and lyrics by John Dempsey and score by Dana P. Rowe. .