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
IJavaProject[] jprojects= jmodel.getJavaProjects();
			for (int i= 0; i < jprojects.length; i++) {
				IJavaProject curr= jprojects[i];
				if (!curr.equals(fCurrJProject)) {
					IClasspathEntry[] entries= curr.getRawClasspath();
					for (int k= 0; k < entries.length; k++) {
						IClasspathEntry entry= entries[k];
						if (entry.getEntryKind() == elem.getEntryKind()
							&& entry.getPath().equals(elem.getPath())) {
							IPath attachPath= entry.getSourceAttachmentPath();
							if (attachPath != null && !attachPath.isEmpty()) {
								elem.setSourceAttachment(attachPath, entry.getSourceAttachmentRootPath());
								return;
							}
						}
					}
				}
			}
		} catch (JavaModelException e) {
			JavaPlugin.log(e.getStatus());
		}
	}
	
	private class AdvancedDialog extends Dialog {
		private DialogField fLabelField;
		private SelectionButtonDialogField fCreateFolderField;
		private SelectionButtonDialogField fAddFolderField;
		private SelectionButtonDialogField fAddContainerField;
		private ComboDialogField fCombo;
		private CPListElement[] fResult;