Thank you for your suggestion.
kf52t- The GPX has to run from DOS if you have other than predefined machinetype, but it still doesn´t give me the same result.
Rebekah-harper- I don´t get the x3g-file from an external g-code. It will only save a new gcode. I do get it from processing a stl-file but I´d like to be able to do some small adjustments.
What I can do is pasting my gcode in the starting script and make an empty run on a stl-file.
This saved a good edited x3g.
But I had some other trouble when doing this so I had to reset all settings.
At least I think that was the reason.