Lin-Manuel Miranda had his rap down at Friday’s party for “Bring It On” at the Dorothy Chandler. “We first opened the envelope with ‘In the Heights,’ and now we are pushing it a little further with this show,” said the songwriter. “With ‘Heights,’ we used rap very specifically. You actually can get away with a lot more with ‘Bring It On’; it’s about a high school and young people.”Although Jeff Whitty’s book departs from the 2000 movie, Miranda said the onscreen montage at the finale was a tip of the hat to that Universal pic. “At the end of the movies, they have a kind of blooper reel, and this was our version of that,” he said. Checking out the screen-to-stage metamorphosis at the Ahmanson was U’s Ron Meyer.