OUTCOME :
I ran my tests. The way I work is that each game level has it’s own Persistent level. So Blue_Persist, and Red_Persist for instance. I load up game levels like Blue_Persist (which loads it’s own lighting and the sub levels it uses). I render shadows and save.
I render shadows in my core game, and then I didn’t even have to re-compile my game, because the World Composition seems to be working well.
My gameplay is error free (shadow-wise).
It took mere minutes to re-render the shadows associated with each level.
Feeling happy with my new setup, took a few days to wrangle it like this, but it will make a huge difference in the time I take to render, and will keep my game together even if I fiddle with individual levels as much as I like, without breaking my game to do so.
It was a week spent well in my studio that will save all kinds of time and lead to a better game, happier developer.