What exactly is the Task Scheduler "custom handler" from the Actions tab?
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/Jq7s4.png)
These are system tasks and you can run the schtasks commands accordingly and search the registry to get more detail (see below quoted text and references).
Warning: You probably could make adjustments to system tasks by manipulating the registry or finding another [hack] forceful to do it, but these are not meant to be modified by users since they are systems tasks so you may hose something up with Windows change these.
You can't view Custom Handlers or Custom Triggers because there's
nothing to view. They're compiled code, in DLL's. They implement the
interfaces defined in the task scheduler API, these are found here:
Task Scheduler Interfaces
(Windows)
You can see which DLL is called by viewing the Task definition. For
example, Badge Update, notice the source is WinStoreUI.dll:
schtasks /query /XML /TN "\Microsoft\Windows\WS\Badge Update"
Because you don't need to edit it. This is not a user task, but a
system task. You can export the task to XML, find the handler GUID,
search regedit for it, etc, etc, but editing it still won't make
sense.
If you want to edit, delete the task and import the modified XML.
Still doesn't make sense, but perhaps it would satisfy those who
insist on editing such tasks. I doubt, though
source
Further Resources