The settings can be made persistent by entering Mainsail’s Interface settings,webcam, and edit crowsnest.conf. The last line:
v4l2ctl: brightness=-16,contrast=16,saturation=56,hue=0,white_balance_automatic=1,gamma=152,gain=0,power_line_frequency=2,sharpness=2,backlight_compensation=1,auto_exposure=1,exposure_time_absolute=260,exposure_dynamic_framerate=0 # Add v4l2-ctl parameters to setup your camera, see Log what your cam is capable of.