I thought:
save the lightmix file (.conf) for each image.
the next morning I open each image with corona image editor and apply the relative saved .conf file to the images
it's correct?
If it's working, then it's correct. :)
You could also try this, but it's a more destructive workflow:
1) Set up your scene with default light settings (not affected by LightMix in any way - so for example white lights, not colored)
2) Save this as a scene state so that you can always return to lights with default non-affected settings
3) Set up your LightMix variant A (for example daylight with dim lights)
4) Use the ">Scene" button to bake LightMix settings into the scene lights
5) Save this as scene state A
6) Load the scene state with default lights
7) Set up a different LightMix variant B (for example nighttime with strong lights)
8) Save this as scene state B
Then you can batch render different cameras with different scene states and each scene state contains different light setup.