Hello, if you want to add new skin to the document and you don't want your existing images to be changed in the other skins, choose Ignore
instead of Replace
.
It is also important that the new skin doesn't have a name that matches other skins, or it will be detected as being the same skin by the script, which is what I suspect may have happened.
I tested the process of importing new skins in Spine and it worked fine for me on the latest Spine version. If you still encounter problems please send a zip that allows us to reproduce the problem you are experiencing to contact@esotericsoftware.com mentioning this topic.