You can modify element definitions using the Design Rules tab of the Door/Window Assembly Style Properties dialog box. You can access these definitions from the assignments list and from the definitions list:
Any changes you make, including changes to the definition name, overwrite the existing definition. To create a new definition from the assignments list, select New from the Element list. To create a new definition from the definitions list, click the New Division icon, the New Infill icon, the New Frame icon, or the New Mullion icon.