Mp3tag is already able to read a CSV alike text file, and to fill tag-fields with data from the text file.
With some programming effort within some Mp3tag actions, one can also read data from any text file, and write data into tag-fields.
Within the websource section of Mp3tag the reading of JSON sources is already implemented.
See also ...
/t/12836/1
/t/16909/1
https://www.google.de/search?q=site%3Aforums.mp3tag.de+JSON
DD.20160322.0442.CET