When the headlight washers come on they spray the bonnet leaving it looking as though I've driven through a car wash and not stayed for the rinse. Is this normal or do they need adjusting? Can they be adjusted?

can change the frequency in settings, set mine to 1 in ten screen washes... don't know if you can do anything about the volume of liquid though. 

Or just disable the headlight washers via vcds, obdelevent etc.

Mine are similar and it is  bit annoying. 

8 hours ago, ionelmc said:

Or just disable the headlight washers via vcds, obdelevent etc.

Aren't they an MOT / roadworthiness item because of the xenons (silly though that might be)? May cause issues with insurance etc in the event of an accident if so. Worth a check if you are thinking about doing it.