additive overwrite on a joint during statemachine animation

Hey Guys.
I have a character state-machine with a few animations such as idle and a hand wave.

I also have a “look at” object in the world.

I need to add an offset to the neck joint on a trigger to make character look in that direction.

Can I create a state that is not a predefined motion but instead a script or something like that or maybe there a way to add offset to the joint directly?

Thank you
Yury

Looks like LateUpdate() could be used to completely override the animation. Still looking for a method to add an offset.