When you activate your Zodiac stars, you will notice some stars will be listed as giving a "random blessing" and be displayed in blue.
The random blessing will be one among the list of possible blessings.
Until version 2, it wasn’t possible to change those once obtained, and some characters were eventually more lucky than others as they obtained a stronger or more appropriate blessing for their class.
In version 2 you can eventually use 100 Rubies to re-activate the blue stars and change your existing blessing to another one from the list.
It may not be worth it for the lower zodiac constellations as the blessings may be small, but can be interesting for a few stars.
Just tap the blue star, then the "Re-activate" button.
You will then see the list of blessings which can be obtained. If you confirm and tap re-activate, you will then obtain one of the blessings from the list at random. Each have the same probability to be rolled, so you may also get the same one!
Example above: each blessing has 20% chance to be obtained (1/5), you may get better, or worse.
The concept is overall similar to the re-enchant system.