Suspending a shutdown might sound like a great feature but from a coders point of view, it would be frowned upon. It is possible but hardly used. CCleaner could override WndProc, WM_QUERYENDSESSION & WM_CANCELMODE etc but this feature won't ever be added to ccleaner. You trigger shutdown then forcing the program to suspend it. Terrible idea.
This is taking into account documentation well before Windows 10, I have no need to investigate I would still work because the whole concept of a programmer suspending this is not o One who cares about system integrity.
The programmers behind CCleaner would have implemented such a feature already if it was deemed application effective. While Microsoft allows us to identify shutdown it just ain't going to ever be implemented.
Commandline (again if still able in W10) can "abort" in command line ""shutdown.exe", "/a"" under the forms closing method. AGAIN this is abuse toOk i had to check, since vista it's no longer used?(thinks) windows. But in vista ShutdownBlockReasonCreate was created.
I dont have time right now to research, but as said 3 times plus. This won't ever be added. Any programmer worth his salt would not even try.
Hope that helps for you. https://msdn.microsoft.com/en-us/library/ms700677(VS.85).aspx?f=255&MSPPError=-2147217396