That's simply not true. However, you must have an EXCELLENT reason to do so (UCSF is a better school is not a valid reason).
Generally, the procedure works like this.
1. Contact the Assist. Dean of Students or full Dean of both colleges and detail your plans.
2. Applications are generally truncated in this instance.
3. Hardship transfers are universally accepted between the AACP schools.
4. For academic transfers, it depends on grade, status, and space available at the incoming school.
This only works for didactics. In the clerkship portion, you should have already worked this out. Transferring is unusual, and in general, student lose credits by doing so. My class has two from St. Louis, and we lost two to Creighton's online program, and Worchester.