I think you're trying to do this in an extremely complicated way. You might find you get much faster results keeping things very simple. The splitter-combiner is useful for some things, but it's not what I'd pull out for a situation like this.
I frequently pull a key on skies just by qualifying the highlights, tracking a shape on just the sky so that nothing else is affected, keeping the key soft (and with some NR if possible) to minimize any "choppiness," and then very subtly lean it in the direction I want with Primary gain. Sometimes multiple shapes are necessary if I want to keep the clouds white. Anything more than that, I'll go for sky replacement provided there's time and money to do so.