iRule to replace http response data

If you just want to replace content in the HTTP response, then I would use a Stream profile and a basic iRule.

when HTTP_REQUEST {
  STREAM::disable
}

when HTTP_RESPONSE {
    set oldString "Next line in readAODResponseStatusCode - 0"
    set newString "Next line in readAODResponseStatusCode - 0000"
    STREAM::expression {@$oldString@$newString@}
    STREAM::enable
  }
}