1. You don't need a script, just one line of code. Put this in your init.sqs
0 setOvercast (random 1)
Syntax not guaranteed.
2. You don't even need a script. The rescource has to be defined in description.ext, right? Part of the definition (called duration I think) is the time the resource for which the resource will be displayed. Set it some huge number and, as long as you don't display another resource, it will stay there the whole time.
Oh, and
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