Alter the index/server settings before creation

I need to specify a french stemmer on my indexes

Like this :

{
  "settings": {
    "analysis": {
      "filter": {
        "french_elision": {
          "type": "elision",
          "articles": [
            "l", "m", "t", "qu", "n", "s", "j", "d"
          ]
        },
        "french_stop": {
          "type": "stop",
          "stopwords": "_french_"
        },
        "french_stemmer": {
          "type": "stemmer",
          "language": "light_french"
        }
      },
      "analyzer": {
        "french": {
          "tokenizer": "standard",
          "filter": [
            "lowercase",
            "french_elision",
            "french_stop",
            "french_stemmer"
          ]
        }
      }
    }
  }
}

I don't see how to push the additionnal settings before that the server/index is created.

Is there a hook function to achieve this?

Thanks.