I have a Catian captain. You all just jealous because the womens keep petting him instead of you :P
And no, you can't change your species after creating one, save for if you went for the full alien creation and go for costume change. That allows you to change facial features and body features. In a sense that one has no base species to set in stone so you can change it all you like for energy credits but that can be rather expensive. I changed a rank pin, just a rank pin and it ended up costing 3,000EC.