CLASS REBUILD: With this command, certain classes can change their class to another. They are effectively rebuilt from the ground up and will have to re-train and re-practice skills as a "new" character. Those classes which qualify due to being grandfathered can rebuild into an equivalent level.
RACE EVOLUTION: With this command, certain races can evolve from one race into another. They maintain their level and are remade into their new image. Like classes, this will require retraining and repracticing. This is a serious decision and those who use the rebuild command cannot go back to their old class. Rebuilds are final.
See also Evolutionary Races.