Adding a normalizer for case-insensitive search on keyword field to an active index

Elastic Stack Elasticsearch
3

Thanks @jimczi

But I'm unable to add a normalizer on an existing index. (I am able to do this for analyzer, but that doesn't work for keyword fields).

curl -XPUT localhost:9200/ganesh_index/?pretty -d '
> {
>   "settings": {
>     "analysis": {
>       "normalizer": {
>         "useLowercase": {
>           "type": "custom",
>           "filter": [ "lowercase" ]
>         }
>       }
>     }
>   },
>   "mappings":{
>      "ganesh_type":{
>         "properties":{
>            "title":{
>               "normalizer":"useLowercase",
>               "type":"keyword"
>            }
>         }
>      }
>   }
> }'
{
  "error" : {
    "root_cause" : [
      {
        "type" : "index_already_exists_exception",
        "reason" : "index [ganesh_index/mg5TckzaR5KZDE-FphTeDg] already exists",
        "index_uuid" : "mg5TckzaR5KZDE-FphTeDg",
        "index" : "ganesh_index"
      }
    ],
    "type" : "index_already_exists_exception",
    "reason" : "index [ganesh_index/mg5TckzaR5KZDE-FphTeDg] already exists",
    "index_uuid" : "mg5TckzaR5KZDE-FphTeDg",
    "index" : "ganesh_index"
  },
  "status" : 400
}