More than likely it's not a CoreRPG layered ruleset. That's unfortunate. But, Zacchaeus seems to think it is so it should work.
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Just checked it now. It shows up as <Option Set> at the bottom of the Options list. It starts as a default of "off" for "Otpions: User Id"
It seems to work well enough. :)
GURPS is CoreRPG based.