Can I set a variable to inherit its value from the folder card ... sometimes?

Can I set a variable to inherit its value from the folder card AND override any existing value ONLY THE FIRST TIME IT IS CHECKED INTO THE VAULT?  If I change the folder variables later, and push them back down to the children, I don't want this variable to update.  I know I can set it up so it will always inherrit the folder variable.  I think I can select which variables to push back down thru the wizzard and control it that way, but I can't think of a way to block that update for this one variable so users cannot accidently overwrite it.  I want it to stay what it is originally set to now and forever.

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