There's a post from some time ago about changing the way night and day transitions work in Divine Divinity (http://www.gog.com/en/forum/divine_divinity_series/solution_for_a_better_alternation_of_day_and_night).

It got me wondering, is there a full list somewhere of all the config options that can be added to these files? It would be interesting to see what other tweaks are possible, especially any "undocumented" ones.

There is no such list, that I know of. There are a couple options that can be used for graphics problems (colour splotches at night or underground, or loss of the dusk/dawn effect). In the disk version there was an option to increase the number of quicksaves used, but that was removed from the download version.

Thanks for the info!

Somewhat related question:
The resolution settings in config.div affect the resolution of the game. But there's another set of resolution settings in config.lcl. Changing those doesn't have an obvious effect. Any idea what they're for?

No, I don't know what the resolution in the config.lcl file is for.