It's one of those uncommon animation names that World Editor nor the Wc3 engine don't recognize very well (like the bla animations from the Storm, Earth and Fire Pandarens). You can only see these animations in model viewers and editors (Magos War3 Model Editor for instance).
The only way I know how to make the alternate animation work is to edit the model and rename that animation to a more compatible name such as "Stand Alternate" and import the edited model.
And yes, this involve a filesize increase in your map.
Perhaps there's an alternative way where you could do some trigger tricks to activate that animation, but I'm no expert of triggering stuffs. So I don't know.