If you have a Spine project file, you can of course open it in Spine, export it, etc. There are some Spine projects for sale on various marketplaces, like the Unity asset store.

3D skeletal animation is very straightforward, the real movements are described in their entirety in three dimensions. In 3D you can use "retargeting" to transfer an animation to a completely different skeleton and get pretty decent results.

For 2D, a lot of "tricks" are used to get the look you want, or to simulate 3D objects. Due to that it is often difficult to make use of skeletons and animations for a different rig. You might instead use a project as a foundation and make modifications to it until you get the different rig that you want.

There are ways to use a single rig (skeleton) and its animations in Spine with many different looks. That is done using skins. Skin constraints can be used to move bones based on which skin is active, so different skins can have different proportions (and more).
Skins - Spine User Guide