Good shout. More if you use the starseers reroll on it. Actually 5/9 chance of moving so more than half. Not bad. With +2 to charge and then rerolling you actually have 92% chance of getting into combat. Not taking into account that you could just reroll 1 of the charge dice using starseer. So basically its prob over 95%
Yeah and changing them is quite risky. Happened to me more often than not. The good thing is that nowadays all three constellations are useful for something.