How to trigger/run/execute scheduled task manually? Is there a way to run a scheduled task manually without any programming? 

If not, this way seems not to work properly Manual execution of scheduled rule. 
After executing a rule, having another one on the list, clearing caches and running the cron, this feature automatically disappears somehow. There is something wrong in the code.
This is how i do it, I use flags module, i create a user flag for each  "run manualy my special rule" assigning flag/unflag access only to admin user and i display link on user profile page, flagging or unflagging myself to trigger my special rule, then, most of the time i use views rules module to load content, products, orders or users and perform any kind of stuff with it.