[geezer#99]

I've done it while running for years.
Can be a bit messy.
Make some cardboard deflectors to keep the oil from splashing too far.
Also do this.
Adjust all of them like TJ says but don't tighten them 1/2 turn right away. Once they're all quiet. shut the motor down and then give each one a 1/2 turn.
Less chance of the motor wanting to quit that way.