NEET PG, an apparent technical glitch at prometric site allowed users to reschedule the test. Here is the press release from NBE regarding the same.

National Board of Examinations

Subject : Clarification regarding Re-Scheduling

Applicants may kindly note that there is no provision for rescheduling in the registration for NEET PG. Please refer to information bulletin and the caution notice mentioned therein. NBE/NEET PG have never advised for any rescheduling option nor prescribed any website or URL for this purpose.
Direct access of the third party websites or server is an act that is neither prescribed nor permissible.
Those who have attempted to do so by accessing the back end system of the third party agency are at their own risk and peril, NBE /NEET PG takes no liability for this act of rescheduling undertaken by any candidate.
Ordinarily this act would classify for appropriate action, however, taking a sympathetic view, NBE is not taking action against any such candidates i.e. their candidature is not being cancelled.
Further, due to this intervention by some candidates, they may have lost their earlier appointment for test, NBE is in the process of scheduling such candidates, however, this is subject to current availability of test center seats.
Applicants are once again advised to refer to information bulletin and refer only to official website for latest updates or contact candidate care for any clarifications (details available at contact us page on website).
Kindly note: entry to test centre shall not be permitted under any circumstances by submission of any false or fallacious document/email.