Can Curator filters documents during reindexation?

The answer to this is a resounding yes. Curator just uses YAML syntax to do anything that you can do with the regular reindex API.

For example, given this JSON reindex block:

POST _reindex
{
  "source": {
    "index": "twitter",
    "type": "_doc",
    "query": {
      "term": {
        "user": "kimchy"
      }
    }
  },
  "dest": {
    "index": "new_twitter"
  }
}

You would create a YAML request_body like this:

request_body:
  source:
    index: twitter
    type: _doc
    query:
      term:
        user: kimchy
  dest:
    index: new_twitter