Leonato is at the center of events from beginning to end. After the formal welcome of Don Pedro, we tend to forget that Leonato is the governor of Messina, at least until he is asked to consider the fate of Dogberry's prisoners. Leonato lets himself be guided rather easily by the ideas and opinions of others: First, let Hero marry Don Pedro if he proposes. That not being the case, let her marry Claudio (even push the wedding ceremony along when it begins to lag). When Hero seems to prove promiscuous, believe the accusers (after all, they are noblemen) and threaten Hero. When the friar offers another approach to discovering the real villain, accept it enthusiastically (after all, the church should know). When he meets Don Pedro and Claudio, challenge them. When everything seems resolved, encourage Beatrice to marry Benedick. And finally, when Benedick suggests dancing before the wedding, try to insist on the wedding first, but when that doesn't change Benedick's mind, go along with the dancing. And worry about punishment of the culprits another day.
Is Leonato changed? Not outwardly, although he may have greater faith in his own daughter and less respect for so-called nobles.