guaxinim_raccoon Your question itself is about the operation of the editor, but I thought it was actually a matter of the way it was implemented on Unity, so I changed the tag to Unity.

Actually, there are our official recommendations on how to improve the performance of loading and rendering skeletons when there are a large number of skins and a large number of textures to load:

• To improve loading times, you can use our Spine Addressables Extension module. This covers all the necessary steps to automatically replace your textures with low resolution dummy textures and load the high resolution textures on demand. For more information, see the following documentation on GitHub:
  EsotericSoftware/spine-runtimestree/4.2/spine-unity/Modules/com.esotericsoftware.spine.addressables/Documentation

• To reduce the number of draw calls you can repack textures at runtime using the Skin.GetRepackedSkin() method. This combines used texture regions of a collected skin to a single texture at runtime. See the Runtime Repacking section of the spine-unity runtime documentation for more information:
  https://esotericsoftware.com/spine-unity-main-components#Runtime-Repacking

It is possible to pack multiple texture atlases in the way described by Spinebot, but you will still need to update the skeleton data each time you make changes to the skin. So instead of having separate skeleton data for each skin, it is better to keep them together, but load lightweight dummy data when the skin is not actually needed.