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Basically, drop binary into mod directory and run it to obtain mod-settings.json from current mod-settings.dat.
Factorio converts mod-settings.json to .dat at startup if the .dat file does not exist.

Btw there was a legit reason why file format was changed, conversion back and forth might result in difference in float values in some cases.

A lua based converter would be nice, but yours is also nice because of readable code.

Which fool would download a binary from the internet without knowing what it does