post https://try.count.ly/i/pushes/push?api_key=
This endpoint allows adding a set of users defined by args.userConditions and args.drillConditions to existing transactional message of _id specified in args._id.
Note that existing notification must be active (or Scheduled in dashboard, result.status & 2 > 0) and transactional (tx === true).
Users are added to the queue right away, meaning scheduling part is done during request processing, not in a detached job way as in /create request.
Returned object shows how much push notifications has been added to the sending queue (total) as well as closest date on which they'll start being sent (next).