I doubt that you could go back to a lower level. Maybe with a save game you could go back and do things differently but not ingame.
What I've read you cannot specify a gender.
I read you can only play the earlier levels (before spaceflight) for a couple hours. I think you could play these levels longer, by not inventing...
Interesting question. But I really shouldn't know. It would be nice though. Looking at the Sims game (where you can switch families) you should...
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