Hi folks, as announced here is the GitHub for the GCODE-Mixer app.
You can download it or run directly on GitHub.
I added some customization functions based on what I read above so in the advanced options of the app you can define specific lines which should be disable in the processed GCODEs. I can imagine this could be usable to speed up the preparation routine of the printer by disabling leveling and other calibration in the follow up jobs.
I tested it already and everything seams to work just fine but I would say the app is still in a beta stage, so may be it will be reasonable to keep an eye on what it throws out, at least at the beginning 
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