There are multiple .sav files which contains:
1 seedName
2 seedNumber
3 sectorsArrY
4 sectorsArrYned
5 characterTransform
6 itermsIndexes
7 itemsCounts
8 controlRotation
9 customSettings
1+2 generation seeds for noise
3+4 state of all voxel changes
5+8 position and rotation of character
6+7 inventory types and count
9 graphic settings
You can add your values there. To check whole logic start from SaveGame widget CreateSaveGameObject