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 CPListElement[] chooseJarFiles() {
		Class[] acceptedClasses= new Class[] { IFile.class };
		TypedElementSelectionValidator validator= new TypedElementSelectionValidator(acceptedClasses, true);
		ViewerFilter filter= new ArchiveFileFilter(getUsedJARFiles());
		
		ILabelProvider lp= new WorkbenchLabelProvider();
		ITreeContentProvider cp= new WorkbenchContentProvider();
		ElementTreeSelectionDialog dialog= new ElementTreeSelectionDialog(getShell(), lp, cp);
		dialog.setValidator(validator);
		dialog.setTitle(NewWizardMessages.getString("LibrariesWorkbookPage.JARArchiveDialog.title")); 
		dialog.setMessage(NewWizardMessages.getString("LibrariesWorkbookPage.JARArchiveDialog.description")); 
		dialog.addFilter(filter);
		dialog.setInput(fWorkspaceRoot);
		dialog.setInitialSelection(fCurrJProject.getProject());		
		if (dialog.open() == dialog.OK) {
			Object[] elements= dialog.getResult();
			CPListElement[] res= new CPListElement[elements.length];
			for (int i= 0; i < res.length; i++) {
				IResource elem= (IResource)elements[i];
				res[i]= newCPLibraryElement(elem);
			}
			return res;
		}
		return null;
	}
	
	private IContainer[] getUsedContainers() {
		ArrayList res= new ArrayList();
		if (fCurrJProject.exists()) {