For about two weeks, Kacy Claassen, 28, was living life as a high school student. She had a fake name, a fake backstory, and a school-issued ID. She thought of almost everything, except making her Facebook profile private. Last month, Claassen walked into Westchester Square Academy in the Bronx and enrolled as Shamara Rashad, a 16-year-old who had just moved to New York from Ohio with her sister. She attended classes, got issued a school ID with…