Thanks for you advice Mudbill, but there´s a warning not to determine too many as FullGameSave, so I don´t think that´s the intended solution to safe things.
Here´s what i did in the meantime:
I set up two maps. Each with a plane, light, start area, 1 button with a callback "Map_ChangeMap(...)". (nothing else in the script)
On the first map are also a lever, a button and a light. Each one can be switched.
Checked for mistakes in the dev.bat. Got no errors.
So i checked the map in the mod launcher.
Result: I start on map1, switch lever,button and light, go to map2, return to map1 and nothing is how i left it behind.
Btw: Thanks for your help guys, really appreciate it