Nick wroteHowever, I do recall some discussion like there could be a dropdown to add animation once the spine object is bind to the track.
This is not implemented yet, sorry. Drag&Drop of an Animation Reference Asset
to the timeline position is currently the quickest way.
Replacing an animation at a clip with another one of the same skeleton is best done as follows (unless someone knows a better way):
1) clicking the currently assigned AnimationReference
asset in the Clip's Inspector so that the Project panel focuses and highlights it, and then
2) dragging the desired animation (usually close to it) from the Project panel to the parameter.