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/ClasspathContainerWizard.java
private ClasspathContainerDescriptor fPageDesc;
	private IClasspathEntry fEntryToEdit;
	private IClasspathEntry fNewEntry;
	private IClasspathContainerPage fContainerPage;
	/**
	 * Constructor for ClasspathContainerWizard.
	 */
	public ClasspathContainerWizard(IClasspathEntry entryToEdit) {
		super();
		fEntryToEdit= entryToEdit;
		fPageDesc= null;
		fNewEntry= null;
	}
	
	/**
	 * Constructor for ClasspathContainerWizard.
	 */
	public ClasspathContainerWizard(ClasspathContainerDescriptor pageDesc) {
		super();
		fEntryToEdit= null;
		fPageDesc= pageDesc;
		fNewEntry= null;
	}