Yes, you can use separate tracks and then blend between them via the TrackEntry.Alpha property.
Additionally, when setting TrackEntry.TimeScale = 0 plus TrackEntry.TrackTime = <target time position in 0..1> you can stop playback and directly set the timepoint of the still-frame of each track.

The following working component code shows how this can be acomplished, having three sliders - one slider for blending between the two layers of animations and two more for each track's TrackTime:

using UnityEngine;

public class MixAnimDirectControl : MonoBehaviour {

   private Spine.Unity.SkeletonAnimation skeletonAnimation;
   private Spine.TrackEntry track0;
   private Spine.TrackEntry track1;

   [Range(0, 1)]
   public float blendToTrack1 = 0.0f;
   [Range(0, 1)]
   public float trackTime0 = 0.0f;
   [Range(0, 1)]
   public float trackTime1 = 0.0f;

   void Start() {
      skeletonAnimation = this.GetComponentInParent<Spine.Unity.SkeletonAnimation>();
      track0 = skeletonAnimation.AnimationState.SetAnimation(0, "jump", true); // simple example, works with the Raptor Spine sample character
      track1 = skeletonAnimation.AnimationState.SetAnimation(1, "walk", true);

  track0.TimeScale = 0.0f;
  track1.TimeScale = 0.0f;
   }
   

   void Update() {
      ApplyTrackParameters();
   }

   void ApplyTrackParameters() {
      //track0.Alpha = 1 - blendToTrack1; // not needed since it's the first track
      track1.Alpha = blendToTrack1;

  track0.TrackTime = trackTime0;
  track1.TrackTime = trackTime1;
   }
}

You modified my sample code a bit too much - you always set the animation at track index 1 instead of one animation at index 0, the other at index 1:

track0 = skeletonAnimation.AnimationState.SetAnimation(1, "rire", true);
track1 = skeletonAnimation.AnimationState.SetAnimation(1, "rire2", true);

It should instead be:

track0 = skeletonAnimation.AnimationState.SetAnimation(0, "rire", true);
track1 = skeletonAnimation.AnimationState.SetAnimation(1, "rire2", true);

Same applies to the block below.

Great to hear that it now works! I just wrote the posting a few minutes before you edited the posting above, so you can ignore it in the meantime.

There is no easing when you directly set the track Alpha values.

I guess the problem is that you are blending between animations by angle which interpolates positions linearly - what you would like is achieved by using the sine of the angle as input, so replace every occurrance of angle by Mathf.Sin(Mathf.Deg2Rad * angle).

Bekko wrote

I created a quick version to make it available "SpineFAce.zip"
my problem, I'm trying to make it full 360, to get extreme angles from above or from below,
but I struggle, it seems like there is a limit of alpha track ?

I cannot yet see what the problem is that you are facing. Could you please describe what your expected outcome is and what you are currently seeing instead?

Glad to hear you could resolve the problem, thanks for letting us know!