maasha ha scrittoSkeletonGraphic
TrackEntry trackEntry = skeletonGraphic.AnimationState.SetAnimation(trackIndex, "animationName", false);
trackEntry.TrackTime = trackEntry.AnimationEnd; //Sets current trackTime to the end of the animation
trackEntry.TimeScale = 0;
Another option would be to duplicate your arms-crossed animation and make a single-frame "pose" using the last frame, and then just use that instead.
Also, if you want it to snap from whatever the previous animation was on that TrackIndex, you'll need to set the mix time to zero.