Scott's, engine off advise is very good advise if you do not
feel comfortable with the engine running at idle... I just
insure the plane is held well.. and be very conscious of
what your doing.. And I make adjustments at idle.. or
you could buy or grind down the working end of a long
screw driver so as the end is outside the end of the prop.
But if you do not feel good about it, adjust with the engine
off.. It'll take a bit longer... But it's safer!!