ArchiCAD removed F1 as a shortcut key to allign with all other Windows Applications and made it exclusively for "Help". You cannot reassign this within ArchiCAD (as far as I know).
I have always used F1 for split and I'm really used to it so I downloaded a free app called "KeyTweak" by Travis Krumsick. (sorry I've lost the url). This app lets you reassign keys on your keyboard. I simply reassigned F1 to F9 and programmed Split to F9 in ArchiCAD. Now when I press F1 the computer instead thinks I pressed F9 and executes the split command. Note: This is not application specific so F1 will no longer work in any program. F9 remains F9 unless you remap this also.
PS: This would make a cool prank, you could remap a few keys on a friends keyboard, it'll drive them mad.