heres a quick walkthrough - i must admit this one had be stumped...
what you want to do is on your shortcut on the desktop (this is how i did it) right click and select properties...
where it says 'Target' it should read something liek this:
"C:\Program Files\Codemasters\OperationFlashpoint\FLASHPOINTRESISTANCE.EXE"
to the end of this add:
"-mod=hisky
so it now reads:
"C:\Program Files\Codemasters\OperationFlashpoint\FLASHPOINTRESISTANCE.EXE" -mod=hisky
then click 'apply' and then ok.... and then to use the mod u have to use the shortcut each time... bingo