Not touch a hair on (one's) head phrase
To not in any way harm or injure someone.
Mark won't touch a hair on Jessica's head because he loves her.
I offer him a truce. I won't touch a hair on his head if he tells me where my gold is.
"Don't touch a hair on his head, or I'll shoot you", the woman shouted angrily.
Beat someone up
To make one feel extremely upset, hurt or offended
If you do something dangerous or risky, you will get hurt.
Try to avoid to change something because doing something else could make things worse
I could have changed my answer, but I decided to leave well enough alone.