Benchmarking search performance with randomised queries

I want to use Rally purely to benchmark search performance as is described here.

In order to simulate realistic search conditions I'd like to vary my query during the search operation, for example if my operation looked like this:

{
  "challenge": {
    "name": "just-search",
    "schedule": [
      {
        "operation": {
          "operation-type": "search",
          "index": "_all",
          "body": {
            "query": {
              "match" : {
                "message" : {
                  "query" : "message1"
                }
              }
            }
          }
        },
        "warmup-iterations": 100,
        "iterations": 100,
        "target-throughput": 10
      }
    ]
  }
}

Am I able to change message1 so that it changes between requests to avoid caching in my benchmarks?

Thanks in advance.

Found my answer not long after posting.

https://esrally.readthedocs.io/en/stable/adding_tracks.html#custom-parameter-sources