Unable to UpdateByQuery via Java API when adding "sort" to existing field

[luicir (Luigi Cirillo)]

I want to avoid reindexing all documents after a field mapping being changed from (excerpt from the template file):

   "subject": {
              "type": "string"
            },

to:

"subject": {
          "type": "string",
          "fields": {
            "sort": {
              "type": "string",
              "analyzer": "ducet_sort_subject"
            },
            "sortConversation": {
              "type": "string",
              "analyzer": "ducet_sort_subject_conversation"
            }
          }
        },

my java code latest version is the following:

PutMappingResponse putMappingResponse = client.admin().indices().preparePutMapping(indexName)
        .setSource("{\"properties\": {}}").setType("email").execute().actionGet();

      BulkIndexByScrollResponse bulkIndexByScrollResponse = INSTANCE.newRequestBuilder(client).source(indexName).get();

Please note that there is no unmappedType default, so if the mapping is not found, I'm expecting to see some error, (as it does without these new lines). Instead I get the results back also for unindexed documents, but the order is random.

I have also tried to add the mapping manually in the setSource above, but result didn't change.

In the documentation I read two statements that seem to be contrasting:

"The simplest usage of _update_by_query just performs an update on every document in the index without changing the source. This is useful to pick up a new property or some other online mapping change."

and

"Templates are only applied at index creation time. Changing a template will have no impact on existing indices. When using the create index API, the settings/mappings defined as part of the create index call will take precedence over any matching settings/mappings defined in the template."

is it even possible to do what I want without reindexing?