Adsense say as follows :
This new ad management feature means that your ad unit settings (such as colors and channels) for new AdSense for content ad units will be saved in your AdSense account every time you generate ad code. Then, if you’d like to change any of these settings in the future, all you do is make the update within your account — you’ll no longer need to manually replace the ad code on all of your pages. For instance, you can quickly change the borders of all your 300×250 medium rectangles from red to blue with just a few mouse clicks. Fancy! We hope that this new feature will help you save time and will simplify the process of optimizing your ad units.
Although this is not yet available. Adsense is continually updating the system and I belie within A week or two it will available to other users.
Last 2 days I have seen some irregularities in my AdSense report maybe this explain the matter. BTW the irregularities increases the amount I earn for the last 2 days. 🙂
Great changes from Adsense.
More information from AdSense site : Inside AdSense: Coming soon: Make ad changes without replacing code