Solutions
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icanttellyou's post in Does MCGalaxy allow for saving in .mine/CW format? was marked as the answerThe MCGalaxy and by extension the MCSharp/MCLawl/MCZall/MCForge (not redux, that uses it's own level format with 16bit block arrays and without the extension data) level format is documented here.
Besides that, MCGalaxy does have a framework for exporting levels to different formats, although that never ended up being used.