Additively adding Expressions to Facial Recording

Hello lovely people,

I am currently looking for ways to simplify the process of adding more expression or general refinement of my facial recordings. I found the Facial Expressions repository in the metahuman folder and had the idea to add these additively to my facial recording animation for subtle improvements. But currently I am only able to paste keyframes that fully replace the facial movements. Does anybody know if this possible, or if there is a better way to clean up and refine the facial recordings via live link face?

Kindest regards,
Habib