I kinda don't think so.
This is for 0.9.7.4, that have already been released. So yeah, if you think CO2 levels on this version are incorrect and you want to ask SpaceEngineer to change the code of atmosphere-composition, you can do it in the thread for the next version.
there are almost no breathable worlds in SE.
That's exactly like in reality, you can't just land on a planet and start breathing just because there's oxygen, the concentration must be in the same amount of that of Earth, a too high concentration would make you pass out, or eventually die, while a low concentration wouldn't give you the oxygen you need.
As a final note, I can't tell if the levels of CO2 in SE are too high or too low, since we have no data!