Well there is a trick to making asymmetric creatures on spore (where their design isn't the same on both sides). Before, the only 2 creatures in spore that were asymmetric were the Grox and Amphiticipate (close enough). But then Maxis released a patch for the game where you could create asyemmetric creatures by holding down the "A" key.
As for the mods.... Well, installing Dark Injection to the data files is easy, but I'd recommend keeping a copy of the saved games cache in case the mod glitches your saved games.
Oh...I didn't know about any of that XD Good to know though! I've always wanted to make them asyemmetric and stuff...I shall try it out :3 Thanks for telling me about all this stuff! 8D enhancing my spore skills X3 I really need to start playing that game more again