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/LibrariesWorkbookPage.java
private ClasspathContainerDescriptor[] fDescriptors;
		public AdvancedDialog(Shell parent) {
			super(parent);
			
			fDescriptors= ClasspathContainerDescriptor.getDescriptors();
			
			fLabelField= new DialogField();
			fLabelField.setLabelText(NewWizardMessages.getString("LibrariesWorkbookPage.AdvancedDialog.description"));
			
			fCreateFolderField= new SelectionButtonDialogField(SWT.RADIO);
			fCreateFolderField.setLabelText(NewWizardMessages.getString("LibrariesWorkbookPage.AdvancedDialog.createfolder"));
			fAddFolderField= new SelectionButtonDialogField(SWT.RADIO);
			fAddFolderField.setLabelText(NewWizardMessages.getString("LibrariesWorkbookPage.AdvancedDialog.addfolder"));
			fAddContainerField= new SelectionButtonDialogField(SWT.RADIO);
			fAddContainerField.setLabelText(NewWizardMessages.getString("LibrariesWorkbookPage.AdvancedDialog.addcontainer"));
						
			String[] names= new String[fDescriptors.length];
			for (int i = 0; i < names.length; i++) {
				names[i]= fDescriptors[i].getName();
			}
			
			fCombo= new ComboDialogField(SWT.READ_ONLY);
			fCombo.setItems(names);
			fCombo.selectItem(0);
			fAddContainerField.attachDialogField(fCombo);
		}
		/* 
		 * @see Window#create(Shell)
		 */