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
protected void configureShell(Shell shell) {
			super.configureShell(shell);
			shell.setText(NewWizardMessages.getString("LibrariesWorkbookPage.AdvancedDialog.title")); 
		}
		protected Control createDialogArea(Composite parent) {
			initializeDialogUnits(parent);
			
			Composite composite= (Composite) super.createDialogArea(parent);
			Composite inner= new Composite(composite, SWT.NONE);
			GridLayout layout= new GridLayout();
			layout.marginHeight= 0;
			layout.marginWidth= 0;
			inner.setLayout(layout);
			
			fLabelField.doFillIntoGrid(inner, 1);
			fCreateFolderField.doFillIntoGrid(inner, 1);
			fAddFolderField.doFillIntoGrid(inner, 1);
			fAddContainerField.doFillIntoGrid(inner, 1);
			Control control= fCombo.getComboControl(inner);
			GridData gd= new GridData(GridData.HORIZONTAL_ALIGN_FILL);
			gd.horizontalIndent= convertWidthInCharsToPixels(3);
			control.setLayoutData(gd);
		
			return composite;
		}
		
		
		/* (non-Javadoc)
		 * @see Dialog#okPressed()
		 */