One of the characters that definitely changed was Alianora, Cimorene's friend. At first, like when he and the other dragons' princesses came to Kazul's (the dragon that kept Cimorene) cave, she was timid. I also thought she was sort of being held back by Keredwel and Hanahh, the other two princesses. However, by the end she was very sure of herself, and helped stop the plot by the wizards. Cimorene changes later on in the series, but not so much now. Someone who really changed was the stone price. He seemed rather silly and didn't know what to do without orders (which I thought weird for a prince) but near the end he showed quick thinking when he melted Zemenar, and he was pretty self-confident (though stuff like that takes time), even when threatened by Antorell.
I liked how the resolution was solved, with Woraug the traitor turned into a frog and the wizards melted but not defeated and everyone living happily ever after. There isn't much I would like to change about the book; it's just too good, but I thought that the court philosopher claiming magic was trickery and smoke and mirrors and the like, given the fact the kingdom was on the edge of an enchanted forest, but I guess some people are like that.
I think the author's message is that rocking the boat is sometimes good.