The following changes will take effect on July 19:

1. The “C” that represents a candidate’s cancelled scores will not be shown on any future GMAT score reports generated by GMAC:
The GMAT exam’s Score Preview feature allows you to make the choice to report or cancel your GMAT score immediately following your sitting of the GMAT exam. In the interest of increasing control and confidence for test takers, cancelled GMAT scores will no longer be included on a candidate’s school report. This change will be effective on July 19, 2015. When a test taker cancels their score, only the test taker will know.
The removal of the “C” on score reports will be retroactively applied.  Any score cancellations done prior to July 19, 2015 will not be included in score reports sent to schools after July 19, 2015.
GMAC cannot remove the “C” designation in school databases from score reports sent to schools prior to July 19, 2015. If the candidate chooses to send another score report, the new report will not include the cancelled scores. Also, only test scores cancelled by the candidate will be removed from score reports. GMAC will continue to report other types of score cancellations, including technical issues or policy violations.

2. Repeat exams allowed after 16 days:
Candidates have the option to retake the GMAT exam after a 16-day time period (versus the current 31-day retake period). This allows candidates the flexibility to retake the exam within a shorter period of time in order to accommodate their schedules, study habits, peak performance times, and/or school deadlines. As always, candidates can’t exceed five GMAT exams within a 12-month period.

For additional details: http://www.mba.com/global/the-gmat-exam/gmat-exam-scoring/cancelling-scores/if-you-cancel-scores.aspx