So I tried to reverse-engineer what Gothi said, but it didn't work.
This is what i did:
I took my PC Saves, added 20 bytes from an Xbox save
Changed the 26th byte to 0x4C (L in ascii) (also saw that in the Xbox save)
And updated the 4 last bytes in the opposit byte order with the Checksum-32 from the 21th byte till the 5 last byte. (I checked the Xbox savegame for that and noticed that it's checksum wasn't from the beginning and was in the opposit byte order)
So... what did I do wrong?