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/SourceContainerWorkbookPage.java
elementsToAdd.add(srcentries[i]);
					}
				}
				break;
			}
			if (!elementsToAdd.isEmpty()) {
				fFoldersList.addElements(elementsToAdd);
				fFoldersList.postSetSelection(new StructuredSelection(elementsToAdd));
				
				if (fFoldersList.getSize() == elementsToAdd.size()) {
					askForChangingBuildPathDialog();
				}
			}
		}
	}
	
	private void sourcePageDialogFieldChanged(DialogField field) {
		if (fCurrJProject == null) {
			
			return;
		}
		
		if (field == fFolderRadioButton) {
			if (fFolderRadioButton.isSelected()) {
				fIsProjSelected= false;
				updateClasspathList();
				if (fFoldersList.getSize() > 0) {
					askForChangingBuildPathDialog();
				}
			}