When you reclassify something, you change its category. A bookseller might reclassify a memoir as "fiction" after it's revealed that the author invented most of the people and events in it.
Your boss where you work part-time may reclassify you as a full-time worker in the summer, when you have more time for your job. And your school might consider cheerleading to be a club, while some others have decided to reclassify it as a sport. In both cases, something has changed categories. The verb reclassify adds the "again" prefix re- to classify, which means "put into a class or group."