code: public boolean replaceSelector( SelectorName original,
                                      SelectorName replacement ) {
          if (original != null && replacement != null) {
              if (selectors.remove(original)) {
                  selectors.add(replacement);
                  return true;
              }
          }
          return false;
      }
docs: Replace this plan's use of the named selector with the replacement. to this plan node. This method does nothing if either
  of the supplied selector names is null, or if the supplied original selector name is not found.
  
  @param original the selector name to be replaced
  @param replacement the selector name to replace the original
  @return true if the replacement was made, or false otherwise