How can someone disable change transparency value of some items in the new KDE 4.10.x? For example notifications and Device notifiers. Someone can hardly read the messages in some occasions.

Which theme are you using? It should not be that transparent.
Also, do you have the Blur effect enabled?

Yes; thank you. It is controlled by the theme. I had the Air theme. I change it to something else and restore it couple of times and it's is ok now.

Anyway i got the same problem a few times since i updated to 4.10, and it seems like Plasma doesn't get composite. Deleting Plasma cache files in home seems to temporary solve, but sometimes it happens again.

@piesko: Please open a separate topic for your issue, so it can be investigated.

This issue:
https://git.reviewboard.kde.org/r/107983/