So I finished this project now. Here is a new slightly shorter video:
It is build with unreal 4.16 for now. I hope 4.19 will fix problems with the lighting scenarios introduced in 4.18 because they are a great feature. In this project you can switch between 3 pre-computed lighting builds: day, sunset and night. The switch takes about 3 seconds. You can also choose between 2 colour variations where most major materials get swapped out with one button click. I made a new interface that supports these two features.
It runs pretty well on a higher end computer. But it also runs with 15 fps on my media PC which has a current generation Pentium (!) CPU with 4GB of RAM and a 2GB Asus GT730 silent video card.