OS2 has a settings component that you can used to save/load values between sessions. Then there's an InitializeForNewMap function in TagGroups that you can use to update things between maps. The advantage of using OS for something like skulls, is if it was built completely in OS without scripts, then it would be map independent and could be used on any SP map the user decides to play.

I was wondering. From what i've heard, using OS script functions on a non OS installation causes an exception, but does this happen when the function is actually used or when the map is loaded? Because if its only when it is used, would it be possible to have a predetermined script global bool (ie one defined in a halo script) that will be false by default but set to true by OS if the user has it? If so this would let map makers use OS functions only when OS is available.