I thought the properties of headlamp couldn’t be edited all along, until I played Buak.
The relevant information should’ve been linked to from the Glasses documentation, but it seems it’s been accidentally left off. 
There’s a few relevant pages:
- Glasses Assets — Unturned 3.x documentation (refer to
Visionproperty) - ELightingVision — Unturned 3.x documentation (refer to
Headlampvalue) - PlayerSpotLightConfig — Unturned 3.x documentation (these properties aren’t unique to the Headlamp, which is why it’s in a separate page)