The Change Workload to: action is not available for the Elapsed Time or Blocked Time exception criteria. The purpose of changing a workload is to put a request where it belongs in the priority hierarchy. Temporary system-wide conditions cause a request to be blocked or run too long. These exceptions do not occur because the request is out of character for the workload.
Elapsed Time or Blocked Time exceptions are better suited to an automated alert. Then the DBA can investigate the system-wide situation and resolve the problem by identifying the cause of the slowdown, rather than punishing the requests suffering from the situation.