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
if (isLibraryKind(kind)) {
				if (!projelements.remove(cpe)) {
					cpelements.remove(i);
					remove= true;
				}	
			}
		}
		for (int i= 0; i < projelements.size(); i++) {
			cpelements.add(projelements.get(i));
		}
		if (remove || (projelements.size() > 0)) {
			fClassPathList.setElements(cpelements);
		}
	}
	
		
	private CPListElement[] createNewClassContainer() {
		String title= NewWizardMessages.getString("LibrariesWorkbookPage.NewClassFolderDialog.title"); 
		IProject currProject= fCurrJProject.getProject();
		
		NewContainerDialog dialog= new NewContainerDialog(getShell(), title, currProject, getUsedContainers());
		IPath projpath= currProject.getFullPath();
		dialog.setMessage(NewWizardMessages.getFormattedString("LibrariesWorkbookPage.NewClassFolderDialog.description", projpath.toString())); 
		int ret= dialog.open();
		if (ret == dialog.OK) {
			IFolder folder= dialog.getFolder();
			return new CPListElement[] { newCPLibraryElement(folder) };
		}
		return null;
	}