public Animator entityAnimator;

    public void OverrideUseAnimation(AnimationClip useClip, string replaceThis) // where replaceThis is the name of the clip/node that already exists in your Animation Controller.
    {
        RuntimeAnimatorController myController = entityAnimator.runtimeAnimatorController;

        if(myController is AnimatorOverrideController) myController = (myController as AnimatorOverrideController).runtimeAnimatorController;

        AnimatorOverrideController animatorOverride = new AnimatorOverrideController();
        animatorOverride.runtimeAnimatorController = myController;

        animatorOverride[replaceThis] = useClip;

        entityAnimator.runtimeAnimatorController = animatorOverride;
    }

// Use it with something like

    public void PlayUseAnimation(AnimationClip useClip)
    {
        OverrideUseAnimation(useClip, "Use");
        SetTrigger("Use");
    }