@traycold: Thank you very much for the Night Mode!!
Night Mode Build 13 works on my Kobo Aura H2O with Firmware 3.15.0
The only issue I see is that if I set "refreshScreenPages = 1" in the nightmode.ini to prevent ghosting at turning the pages it will be set back to "refreshScreenPages = 0" if I check the nightmode.ini the next time I connect the H2O to my pc.
If I change e.g. the brightness level at which the night mode toggles (e.g. from 3% to 34%) the setting remains stable and works as it should.