Try this:
# Credits
outputto "ALBUM_CREDITS"
gotoline 1
regexpreplace "(?:^.*\"extraartists\"\:\[)(.*$)" "$1"
ifnot "{\"id"
regexpreplace "}$" "\],"
regexpreplace "\,\"(images|thumb)\"\:.*?\]" ""
regexpreplace "\,$" ""
regexpreplace ",\"id\":\d+,\"resource_url\":\".*?\"" ""
regexpreplace "\]$" ""
regexpreplace ",({\"name)" "\r\n$1"
replace ",\"tracks\":\"\"" ""
replace ",\"anv\":\"\",\"join\":\"\"" ""
replace "{" ""
replace "}" ""
regexpreplace "\r?\n" ""
regexpreplace "(\"role\":\"[^\"]+\")(\"name\")" "$1<<NEWLINE>>$2"
regexpreplace "\"name\":\"(.*?)\",\"role\":\"(.*?)\"" "$2 - $1"
regexpreplace "<<NEWLINE>>" "\\\\"
regexpreplace " \(\d+\)" ""
sayrest
endif
Instead of the newline split in my code, the above should replace "<<NEWLINE>>" with "\\", the latter being a signpost for splitting the tag into multiple tags. This code is new, as it will need changes if the Credits have specific track information.