The most significant is that the maximum number of boards used to calculate your grade will increase from 1000 to 2000 (around 80 typical sessions). This will reduce the effect that any single session has on your grade and will mean that your grade will have smaller fluctuations.
Green pointed events, and other EBU or national events, currently are weighted triple compared to other events of the same number of boards. Since these events typically mix players from different clubs and areas, the extra weight helps the standardization of grades across the whole of the EBU, very important in the early years of NGS. It is now appropriate to reduce this extra weight from triple to double. All other events will have the normal single weighting.
The NGS has always intended to include only events that took place within the last three years in calculating your grade. Since the first graded events were in April 2010, these old events will start to be excluded from your grade from April 2013 even if you have played less than 2000 boards in the last three years.
Your grade will continue to be regarded as "Mature" if you have played over 1000 boards in the last three years and "Evolving" if you have played between 300 and 999 boards in the period. If you have played fewer than 300 graded boards in the last three years, your tentative grade is not published.
The additional change mentioned above concerns the 15% of EBU members who play as a pair nearly all their graded games with each other. We are adding a mechanism to pull the grades of such pairs closer to each other. This is a gradual mechanism which will take typically another 2000 boards to have a significant effect, so don't expect any sudden change. It will have no effect on you unless you and your regular partner have both played over 85% of the boards contributing to your grades with each other.
For more details on these changes, we will add to the NGS FAQ on the website and to the 'further reading' document in the next few weeks.