Paul,


There is always the "safe" way, of ascertaining the current situation (whether it's rich or lean and by how much...) and stopping the engine to do the adjustment... This goes for both the high-speed needle and the low-speed needle.

But then you would eventually burn out your starter... and it will take you about one year...

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Someone once said there is absolutely no danger in flying. None at all.
It is crashing that is dangerous and you must never do it!...

The same goes for props and mixture adjustments.
You could put your fingers 0.05 mm away from a prop blade spinning at a Zillion RPM and you could never, ever hurt yourself...

But never put your fingers into the prop-arc, even at only 500 RPM... You would get hurt for sure.

It is much easier and faster, to reach the correct adjustment status by being very careful and doing it with the engine running. It is safer, however, to do it with the engine shut-down.