how to change the scale of the sun, without effecting other levels?

Im trying to recreate Nacht der Untoten, fro COD World At War, i want to change the sun to represent the moon, but the moon in nacht is giant for some reason, so i want to change the scale to represent it. when i change the default value of the sun radius node, it does this for every other project, and level. Is there a way i can get this giant moon effect? without it effecting my main project.

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