Combining 2 read only animations

I have 2 imported read only animations. AimDown and AimUp for my character. Both of them are static, so no movement included.

My goal is to make a script that lets my character aim follow the mouse on the y axis. For this i intend to create an animation from the two on top, and call this new animation frame bye frame according to the mouse rotation.

I'd like to create an animation which starts at the AimDown position, and ends at the AimUp position.

Can you help me with this, or is this even possible?

I don't have much experience with Unity, just experimenting right now. And sry for my english :)