Elasticsearch - split nested objects from an index into a new index

Question

I have an index user-stats in Elastic that has documents as follows:

{
  "userId": 1285641,
  "pageVisits": [
    {
      "pageUrl": "/profile",
      "pageName": "My Profile",
      "responseTime": 25,
      "exception": null
    },
    {
      "pageUrl": "/admin",
      "pageName": "Admin Console",
      "responseTime": 12,
      "exception": {
         "code": 401,
         "message": "You do not have permission"
      }
    }
  ]
}

I would like that each time I save a document to the user-stats index, I do some sort of a pipeline that would publish to another index page-visits

{
  "userId": 1285641,
  "pageUrl": "/profile",
  "pageName": "My Profile",
  "responseTime": 25,
  "exception": null
}

{
  "userId": 1285641,
  "pageUrl": "/admin",
  "pageName": "Admin Console",
  "responseTime": 12,
  "exception": {
  "code": 401,
    "message": "You do not have permission"
  }
}

Since I can't change the app that publishes to the first index, I would like to know if I can do something to automatically create my second index, and also update it at each save?

Thank you in advance