Symptoms
Change notification text
Diagnoses
When the user complete task using smartactions he/she receives notification with the form completion text like "You successfully completed the task with the 'ApproveDecline' action."
Resolution
Please have a look at the Templates in the following folder location.
C:Program Files (x86)K2 blackpearlHost ServerBinTemplatesMessages
The files you are looking for would be...
SmartActions.ActionExecuted.htm
SmartActions.ActionExecuted.txt