Yikes, If I had that many to change I'd try to work around the pattern of export/import.
Not the best solution for having a centralized spine file... but,
-What you can do here is after setting up one skin.
-Duplicate the skin the additional 12 or so times. This will make 12 of the same skin setups, but you will have named the skins.
-Export the skeleton to a json file with pretty print.
-Open the json file in text editor and use find and replace next, start your cursor just above one of the skin definitions, and use replace next (not replace all) just enough times that you affect the folder name occurrences in that one skin to the new folder path.
-Change your replace pattern before continuing into the next skin definition and repeat.
-Import the json file back into a Spine project.