Bug 4240 Can't edit class path entry (1GKEPIF)
There is no way to edit an existing entry for a library on the Java Build Path project properties page (other than editing the .classpath file directly). NOTES: EG (9/22/2001 11:42:11 AM) this is particularly annoying for variables. we should have an Edit button when a variable is selected.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/NewContainerDialog.java
private StringDialogField fContainerDialogField;
	private StatusInfo fContainerFieldStatus;
	
	private IFolder fFolder;
	private IContainer[] fExistingFolders;
	private IProject fCurrProject;
		
	public NewContainerDialog(Shell parent, String title, IProject project, IContainer[] existingFolders) {
		super(parent);
		setTitle(title);
		
		fContainerFieldStatus= new StatusInfo();
		
		SourceContainerAdapter adapter= new SourceContainerAdapter();
		fContainerDialogField= new StringDialogField();
		fContainerDialogField.setDialogFieldListener(adapter);
		
		fFolder= null;
		fExistingFolders= existingFolders;
		fCurrProject= project;
		
		fContainerDialogField.setText(""); 
	}