Recently I've wanted to create my own custom codex for the game to add some more stuff to do for myself. I've looked at countless resources, and while some were helpful, most were completely outdated and from years ago. I'd also like to make this so that I can share it with my friends easy over the steam workshop for us to play together with. Thanks in advance for any response I might receive. I'll be back in about an hour to check on this, I'll try and reply to stuff then.
If you never made a starbound mod before, I suggest starting here. http://community.playstarbound.com/resources/unofficial-modding-ebook-2-0.2930/
I'd also recommend http://community.playstarbound.com/resources/template-race-mod.956/ Look at the codex section. If you want it to appear randomly in the game, its needs to be part of a treasurepool. Another way to get it into the game is to make it craftable. To do that, you'd need to make a .recipe for it and patch it to the player file. Hope this helps =3 A really great mod that does this already is the Felin mod. I'd recommend dissecting that for some help!