Hi again. I have now done some testing, and I am sad to report, it seems my original dream is dead. Here is my findings.
It seems to me the checksum you were talking about is in the FileFooterBlock. I therefore made a lot of different r1-files in the stars race wizard, where the only change between files were the growth rate, which I set at all the different values.
Based on these files, I was able to see the pattern in the checksum for this one file. (Another file I tried would give another pattern, I did not try to find out how to generate the checksum at this point, as that would be quite another monster.)
So, after finding out this pattern, Based on reading in the default 19% race with 0 points left, I then wrote two race files via the starsapi project, one with 18% and one with 20% growth rate, and modifying the checksum in the FileFooterBlock to match the pattern while writing the files.
Both of these files are now accepted as non-corrupted files in Stars, they both open fine in the stars race wizard, the 18% race showing 65 points left and the 20% race showing -125 points left.
When I start a new game with the 18% race, everything is fine. Playing a turn does not trigger any hacker flag or anything.
When I start a new game with the 20% race, the race seems to be REPLACED with the default Humanoid-race, with a random name.
So apparently there IS a check at startup checking for negative points (at least for human players), that just replaces the race with humanoids if below zero points left.