Although YOOtheme’s documentation says to store customizations in Widgetkit 2.x:
Place your custom content provider in THEME-NAME/widgetkit/content/PROVIDER-NAME/
Place your custom widget plugin in THEME-NAME/widgetkit/widgets/WIDGETPLUGIN-NAME/
http://yootheme.com/widgetkit/documentation/customizing/where-to-store-your-customizations
It does not explain WHERE to get the original files to modify. In Widgetkit 1.5.x, they were in:
media/widgetkit/widgets/WIDGET_NAME/
However, I just figured out that in Widgetkit 2.x, they are in:
administrator/components/com_widgetkit/plugins/widgets/WIDGET_NAME/
As an example, to customize the GRID widgetkit, you would get
administrator/components/com_widgetkit/plugins/widgets/grid/views/widget.php
and place it into
templates/THEME_NAME/widgetkit/widgets/grid/widget.php
However, if not on a YOOtheme template, you have to overwrite the actual file in
administrator/components/com_widgetkit/plugins/widgets/WIDGET_NAME/
I verified with YOOtheme that you cannot do Widgetkit template overrides in non-Warp templates.
http://yootheme.com/support/question/98708
Hope that helps someone out.