Usually when you preform An action such as shooting or blocking..etcc you should call this event and activate stance.

In the demo I call this event trough weapon system

Once stance is activated modifier to rotation rate is apllied trough.

PDA_MovementSettings

Additionally, you can apply an overlay pose to your locomotion set

PDA_AnimLocomotionSet

by adding the active pose overlay data object

Calling the active stance won't change the rotation mode unless you call "set aiming" or "set rotation mode", this way you can activate stance without affecting the rotation.