Hi ConRAD,

I'm not sure, if your assumptions apply. A bike dynamo is a constant current source, with a current of about 500mA.
You are right, unloaded the voltage can be extremely high, I remember something like ~1V per km/h? But the voltage drops significantly with the presence of a load. To the best of my knowledge it is almost impossible to get more than 10W from a bike dynamo. Are these circumstances suficient to get a significant hazzard for the human body?

Moreover I want to point out two aspects:
(1) The danger to harm your fingers or even to do a front spin with the bike seems to be much more likely than electrical issues, when you perform ajustments like you descriped.
(2) When you cycle faster than -let's say 20 km/h- it is a realy good idea to keep both hands at the bars. People doing dynamo adjustments at 50km/h apply for the Darwin Award. Not because of electrical issues, but because of general safety rules.

And, last but not least, I highly recommend the use of a dynamo hub, which avoids a lot of the drawbacks of the old-fashioned bike dynamos.