>>265384756
So update on this.
I've tried using this command:
C:\SteamLibrary\steamapps\common\SteamVR\tools\lighthouse\bin\win32\lighthouse_watchman_update.exe -D tools\lighthouse\firmware\vr_controller\archive\htc_vrc_dongle_1461100729_2016_04_19.bin

But I get this error:
Supplied file does not look like a dongle firmware. Aborting...