Modify pages widget and make a plugin?

Widgets are class based, so it is quite easy to extend them.

  1. Create your class by extending WP_Widget_Pages (just like it extends baseline Widget).

  2. Copy method(s) you want to modify into your class and make changes in there. You would probably want to extend and modify name and such so it is not confused/conflicted with native widget.

  3. Register your class using register_widget().