Yes, but only in very specific circumstances:

• Your NetID was created incorrectly as a result of a data entry error made by the university.
• There is a personal safety issue related to the continued use of your NetID.
• Your legal name has been changed.
  Your NetID can be changed only after you have submitted your name change request to Human Resources (if you're an employee) or the University Registrar (if you're a student) and they have processed your request.

To request that your NetID be changed, email computer_access@cornell.edu stating the reason for the change.