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 ListDialogField fClassPathList;
	private IJavaProject fCurrJProject;
	
	private ListDialogField fLibrariesList;
	private IWorkspaceRoot fWorkspaceRoot;
	
	private IDialogSettings fDialogSettings;
	
	private Control fSWTControl;
	
	private final int IDX_ADDJAR= 0;
	private final int IDX_ADDEXT= 1;
	private final int IDX_ADDVAR= 2;
	private final int IDX_ADDADV= 3;
	private final int IDX_EDIT= 5;
	private final int IDX_REMOVE= 7;