You have to look into Ape Enhancement and the like files. The sticky above has a tutorial how to use them. I'm using them for the last few years with great succes (meaning without messing up my ZT games).
I have looked around, for the llama and the komodo, use
this file from the Zootycoonabc site.
Shortly:
1. copy your config.ztd (find in C:\Program Files\Microsoft Games\Zoo Tycoon) file somewhere safe (I suggest making another folder for it)
2.delete the file in your ZooTycoon folder
3.take the config.ape file from ApeXP
4.place it in your ZooTycoon folder
5.rename your config.
ape to config.
ztd6.open ApeXP
7.create new project
8.choose llama or komodo dragon
Watch out, if you want to play a game, you have replace your config file of ApeXP back with your
original config.ztd file. That's why you have to have a
copy of it somewhere safe. Otherwise the game will crash.
Also: I've had it, that my created animals won't work correctly. Don't worry, this can be helped by extracted the original uca file of the llama, adding its uca numbers into the file.. etc.. it can be helped, shortly. If you come across the problem, please post and I will help you.