To extend an existing class, create a new class of stereotype Extension; see Working with the Cúram Model in Rational Software Architect for more information on using and modeling with Rational Software Architect.
Options can be added to the extension class in the same way as for other classes. When any of these are added to an extension class they have the effect of adding (if not already existing) or modifying (if already existing) the same named option on the target class.
When creating an Extension class in Rational Software Architect, keep in mind that since it can apply to different class types. You must make sure the settings for the extension class are compatible with the class you are extending.
The extension class is linked to its target class by adding an relationship of stereotype extension between the two classes. The new class should be created within a custom sub-package of your model.