From what I could understand in the original post, I assumed that they wanted yaw control to not have any affect on pitch and roll (relative to the ground plane). Meaning what they wanted was yaw in the world reference plane. To do that easily, I split the roll and pitch apart from the yaw by using local and world rotation functions. I am applying pitch and roll input in the actor local frame and applying yaw input in the actor world frame. The extra code in the top should pull your roll to 0 when no input is applied (I think based on what I remember).