Why change him? I think Picard's traits make him a great character in itself.
People say Picard was different in the movies, well I disagree. What about Captain's Holiday, QPid, Time Squared, Genesis, etc. that all show Picard in an action role? Sir Patrick Stewart himself insisted to the producers that Picard be given a more expansive role. Also an action finale works better in a film, since practically all films are based on the good guy killing the baddie format.