anchor.diff:  `.ds-logs-000001` to the `new_logs` data stream. Note the request's `op_type` is
   `create`.
   
  -////
  -[source,console]
  -----
  -PUT /_index_template/logs_data_stream
  -{
  -  "index_patterns": [ "logs*" ],
  -  "data_stream": {
  -    "timestamp_field": "@timestamp"
  -  },
  -  "template": {
  -    "mappings": {
  -      "properties": {
  -        "@timestamp": {
  -          "type": "date"
  -        }
  -      }
  -    }
  -  }
  -}
  -
  -PUT /_index_template/new_logs_data_stream
  -{
  -  "index_patterns": [ "new_logs*" ],
  -  "data_stream": {
  -    "timestamp_field": "@timestamp"
  -  },
  -  "template": {
  -    "mappings": {
  -      "properties": {
  -        "@timestamp": {
  -          "type": "date"
  -        }
  -      }
  -    }
  -  }
  -}
  -
  -PUT /_data_stream/logs
  -
  -PUT /_data_stream/new_logs
  -----
  -////
  -
   [source,console]
   ----
   POST /_reindex
  
positive.code:     "mappings": {
        "properties": {
          "@timestamp": {
            "type": "date_nanos"                 <1>
          }
        }
      },
      "settings": {
        "index.lifecycle.name": "logs_policy",
        "sort.field" : [ "@timestamp"],          <2>
        "sort.order" : [ "desc"]                 <3>
      }
    }
  }
  ----
  // TEST[continued]
  
  <1>  Changes the `@timestamp` field mapping to the `date_nanos` datatype.
  <2>  Adds the `sort.field` index setting.
  <3>  Adds the `sort.order` index setting.
  ====
  +
  If wanted, you can <<manually-roll-over-a-data-stream,roll over the data
  stream>> to immediately apply the new mappings and settings to the data stream's
  write index. This affects any new data added to the stream after the rollover.
  +
  .*Example*
  [%collapsible]
  ====
  The following <<indices-rollover-index,rollover API>> request rolls over the
  `logs` data stream. This creates a new write index with mappings and index
  settings from the recently updated `logs_data_stream` template.
  
  [source,console]
  ----
  POST /logs/_rollover/
  ----
  // TEST[continued]
  ====
  +
  IMPORTANT: You cannot use these methods to change the mapping of a data stream's
  <<create-a-data-stream-template,timestamp field>>. To change the timestamp
  field's mapping, you must reindex the data stream. See
  <<data-streams-use-reindex-to-change-mappings-settings>>.
  
  * To apply mapping and setting changes to all existing backing indices and
  future ones, you must create a new data stream and reindex your data into it.
  See <<data-streams-use-reindex-to-change-mappings-settings>>.
  
  [discrete]
  [[data-streams-use-reindex-to-change-mappings-settings]]
  === Use reindex to change mappings or settings
  
  To change the mappings or settings for every backing index in a data stream, you
  must first create or update an index template so that it contains the
  changes. You can then reindex the existing data stream into a new one matching
  the template. This applies the mapping and setting changes in the template
  to each document and backing index of the data stream destination. These changes
  also affect any future backing index created by the new stream.
  
  Follow these steps:
  
  
negative.code:   }
  }
  ----
  ====
  
  . If you previously changed your {ilm-init} poll interval, change it back to its
  