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
libaryPageSelectionChanged(field);
		}
			
		
	
		public void dialogFieldChanged(DialogField field) {
			libaryPageDialogFieldChanged(field);
		}
	}
	
	private void libaryPageCustomButtonPressed(DialogField field, int index) {
		CPListElement[] libentries= null;
		switch (index) {
		case IDX_ADDJAR: 
			libentries= chooseJarFiles();
			break;
		case IDX_ADDEXT: 
			libentries= chooseExtJarFiles();
			break;
		case IDX_ADDVAR: 
			libentries= chooseVariableEntries();
			break;
		case IDX_ADDADV: 
			AdvancedDialog advDialog= new AdvancedDialog(getShell());
			if (advDialog.open() == advDialog.OK) {
				libentries= advDialog.getResult();
			}
			break;
		case IDX_EDIT: 
			List selElements= fLibrariesList.getSelectedElements();