code: public static Option[] editConfigurationFileExtend(final String configurationFilePath,
          File source, String... keysToUseFromSource) {
          return createOptionListFromFile(source, new FileOptionFactory() {
  
              @Override
              public Option createOption(String key, Object value) {
                  return new KarafDistributionConfigurationFileExtendOption(configurationFilePath,
                      key, value);
              }
          }, keysToUseFromSource);
      }
docs: This option allows to configure each configuration file based on the karaf.home location. The
  value is "extend" which means it is either replaced or added. For simpler configuration you
  can add a file source. If you want to put all values from this file do not configure any
  keysToUseFromSource; otherwise define them to use only those specific values.
  
  @param configurationFilePath
  configuration file path
  @param source
  property key
  @param keysToUseFromSource
  property keys to be used
  @return option array