The purpose of using archetypal characters in a story is as a storytelling shorthand. The characters appear much more simplistic (less complex) than “real” people, though they still are well rounded (motivations, methodologies, etc.). It doesn’t matter to Dramatica if you reassign motivations after you assign an archetype to a character, providing that you understand that you are thereby making the character more complex and “less” archetypal. We use archetypes in the StoryGuide because it is simpler to lead you (and every other writer who follows it) through the process.