Additive animation for head/eye

Sorry if you've received duplicate email for this topic since I don't know which email I should send my questions to.
I have a professional license for FaceFX Studio 2017.1, and I'd like to ask:

Is there a way to use Eye/Head Pitch/Roll/Yaw curves as additive animation on top of the preview/event animations?
So that I can retain the base animation on head/eye but still get the performance generated by faceFX.
I don't want to set bone weight to less than 1 since that means I get an average value from faceFX curve and base animation, not additive.

Thank you for your help!

I think I understand what you are looking to do, and the only way to do it (in FaceFX Studio) would be to have content with 2 head bones.  Then FaceFX could have 100% control over one bone, and the body animations could have 100% control of the other one.  The results would be additive, so if the body animation turned the head left and FaceFX turned the head left at the same time, you might over-rotate the head.

FaceFX doesn't let you configure the animation blend mode of the bones beyond the bone weights (and bone weight curves) that let you split the animation weight between FaceFX and body animations.  Your mileage may vary in other game engines and animation programs.  You can certainly set up additive blending in UE4 with the FaceFX Runtime, which is great for having a single set of bone poses that work across a wide range of characters with slightly different rest poses.