Change the Animation Clip of a Mecanim State

I'm making an RPG that each character should have a lot of skills, and each skill have different corresponded animation.

Ideally I should store the AnimationClip as a variable in each Skill class, and set only one state in the Animator called "Using Skill". When I use a skill, the clip inside "Using Skill" state should change corresponding with the current skill. However, I can't find a way to set the "Motion" property of a Animation State using script.

Is it possible to achieve this in Mecanim? (Without making tons of state)

Or should I use legacy animation instead?