This is not possible at this time. I will suggest you create a request for Enhancement for this (my guess is there may be plans for this in the future). If you only care about this for one service, you can drill down into the dynamic requests for that specific service and add the filter for "HTTP response code" and select specific response code, you will see a text field to to add the specific status code. The downside to this is you have to do this every time and cannot pin to dashboard.
Hope This Helps