private void alterRegion(Region<?, ?> region, String queueName, boolean synchronous) {
    if (!isAccessor(region)) {
      region.getAttributesMutator().setCacheLoader(new JdbcLoader<>());
      if (synchronous) {
        region.getAttributesMutator().setCacheWriter(new JdbcWriter<>());
      } else {
        region.getAttributesMutator().addAsyncEventQueueId(queueName);
      }
    } else {
      if (!synchronous) {
        region.getAttributesMutator().addAsyncEventQueueId(queueName);
      }
    }
  }
Change the existing region to have
the JdbcLoader as its cache-loader
and the given async-event-queue as one of its queues.
geode-connectors/src/main/java/org/apache/geode/connectors/jdbc/internal/cli/CreateMappingFunction.java