Funny, I am doing the exact same thing. I ran across http://pastebin.com/k91ZpGzi yesterday and was able to create and place the new mortar and pestle. However the problem comes in with overriding the PrimalInventoryBP_MortarAndPestle. Here is where the crafting station lists what its able to craft. When you place your custom mortar the system freaks out because you have removed the old chitin paste from the master list. The inventory object requires the old one and blows up.
So, how does one override the old PrimalInventoryBP_MortarAndPestle with a new one that acknowledges the new paste?