The question is: does MP3tag look into that folder at all or somewhere else e.g. when you installed MP3tag as portable installation.
You can quickly find out which folder MP3tag uses if you create a Tool (File>Options>Tools) which calls the Windows Explorer and opens it in the data path:
Path: C:\Windows\explorer.exe
Parameters: '/e,"'$getEnv('MP3TAGAPPDATA')'"'
Execute this tool and see where the Explorer opens.
The tag source script shoud then be in the folder "sources"