I did not see a practical way to unhook the headlamp. It looks like the wire is permanently attached to the headlamp, and feeds in through the stem and down through the frame. Maybe there is a connector hidden somewhere? Let me know!
Since I planned to relocate the headlight anyways, I just cut the wires about 4cm behind the headlamp. They are color-coded black/red, so you don’t need to label them. I plan to add a front basket, and mount the headlamp on the front of that, so I will need to splice the wiring anyways.
For test rides, I am using a Busch & Mueller ixon iQ Premium. It’s not as bright, but it’s a good light. The bike probably looks less cool. Serial1 obviously put lots of custom parts design work into hiding all those cables. But as it was, it was not rideable by me, so it was either change it or sell it.