Previewing tuner “Shrek the Musical” has canceled its Tuesday perf in order to incorporate changes to the production that creatives would not have had time to accomplish otherwise, according to reps for the show.All other perfs will play as skedded in the run-up to the tuner’s Dec. 14 opening. Specifics about the nature of the changes were not given. Since its out-of-town tryout in Seattle earlier this fall, the developing musical has undergone tinkering that has included the recasting of Donkey, the titular ogre’s sidekick, and the reimagination of the design for the character Dragon. “Shrek” marks the first tuner outing from DreamWorks Theatricals, the legit arm of DreamWorks Animation. Org co-produces with Brit company Neal Street Prods.