1) Can I add anything in toolbar near *file* *view* *help*?
I want to add my own custom option in the toolbar.
2) Can I edit KNIME GUI Component such as *Import KNIME Workflow* UI which opens from *File* tool?
I am attaching screenshot to be more clear.
Tricky. You can't change that wizard page itself.
I think you can offer your own option in the File menu. Follow the class org.knime.workbench.explorer.view.actions.export.WorkflowExportAction
You should be able to declaritively add extensions like shown in /org.knime.workbench.explorer.view/plugin.xml