If you "use Win32" then you can call Win32::AbortSystemShutdown(). You can also "use Win32API::Registry qw( AbortSystemShutdown )" which has the advantage of exporting the function so you don't have to type "Win32::" each time and actually including documentation for the call.

Update: "perldoc Win32" finds the documentation (in perl/lib/pod/win32.pod) but I didn't find it in Win32.pm.