We can use variables to drive the changes in Translation, Rotation or Scale on the Transform Modify Bone to affect our character.
In the video above, the Rotation Value variable drives the rotation of the MF_Spine_01 and b_MF_Neck Bones in our character.
The scale of our character is also driven by a float variable (Scale Multiplier) which affects the spine of our character, increase/decreases the size of the bone and scaling our character.
Bone To Modify
Name of the target bone to modify the Transform of.
A Vector specifying the Translation to apply to the target bone.
A Rotator specifying the Rotation to apply to the target bone.
A Vector specifying the Scale to apply to the target bone.
Transform (Modify) Bone nodes are also affected by the LOD Threshold system introduced in 4.11. You can find the setting for this in the Details Panel for the Transform (Modify) Bone node.