I am currently registered to sit for an exam, but something has come up and/or my plans have changed. Can I postpone my exam to the next testing window?

No, registration is exam-specific and not open-ended. By registering for a single exam, you are committing yourself to a date- and time-specific exam, and you may not postpone from one testing window to another, e.g., you cannot change your September exam registration to March. If you are unable to sit for the exam for which you are currently registered, or if you do not pass, you will need to re-register to take the exam during a future exam window. The fee for reregistering for an exam  is US$795, regardless of whether you sat for the exam the first time.