Found something I didn't expect in JSON "mode".
JSON loads the original API stream and ignores every change done within web script before switching JSON mode "ON".
E.g. just a random fictional example. Add leading Zero to single digit track position regexpreplace "("position": ")(?=\d")" "0"
Track position is still extracted with one digit, that means all stream manipulations are simply ignored.
JSON is a great feature and (I believe) will be the future of web scripting.
Currently it can be used for limited functionality.
Hopefully Development team (Florian???) will amend JSON functionality.