Looking at it, it's actually a todo source/tools/atlas/AtlasUI/ScenarioEditor/Sections/Object/Object.cpp:572
I guess I can inspire myself from https://code.wildfiregames.com/D2042
to make it work.
It should only take the names in the animation blocks for each variant, parent variant and groups
<animations>
<animation event="0.5" load="0.0" name="attack_ranged" speed="100"/>
</animations>