The application is done! I just had to make sure that it's completely reverisble before releasing anything. I have now successfully changed from XEN to XEE and back to XEN.
But as you might understand, messing with system files is always dangerous and the possibility for a brick is always present. Hopefully this will not occur
I'm doing my best to avoid that.
For everyones safety I would recommend doing a manual backup of /system/build.prop and the complete /efs folder including nv_data.bin
The app does this automatically to the internal SDCARD, but just to be on the safe side I would recommend a manual backup to the computer aswell.
There is two steps where a reboot is required between. The app will tell you what to do.
So here it is: SpoofFw - requires ROOT and BusyBox
Direkt market link
If you get problems to connect to Kies after you used this program, try remove the registry key "HKEY_CURRENT_USER\Software\Samsung\Kies\Devic eDB"
Please let me now if it works out for you.