SetIsControl has two parameters, listed as a scan code and a control code in the FOSE documentation. It's used to designate a hotkey as a control key to prevent conflicts with other mods. There's no "setisnotcontrol" command though, so I would guess that you'd use it like this:

SetIsControl scancode 0
or
SetIsControl scancode 1

Where the 0 or 1 sets a flag that determines whether its a control key or not. That doesn't seem to be how the documentation explains it though. Anybody have any experience with it?