In the beginning of the book Jonas is nice and acts perfectly, just like the rest of the people in his community. However, he recieves his job and rules (only because of a failure ten years before) and finds two rules that states how he can break other rules. Jonas does not break the rules, instead he makes sure to follow them. Even when The Giver tells him not to apoligize because it wastes time, he almost slips up over three times. So right now Jonas is a very polite, unknowing boy.
Much later in the book, after Jonas finds out about being "released" and freaks out, it turns his attitude around totally. The night that he finds out about being released he refuses to go back home to his mother and father, mainly because they were ok with what was happening. He even starts to formulate some sort of plan, while lieing to his father as he returns to his house. I think that this shows that he did change (at least his mind set) quite a bit. He went from stick to the rules to pretending he was lost in the river, so he could escape and useing his privleges to their full advantage.