While I, personally, would not edit someone else's creation, I will say that the shelter assignment is in the .xml file located in the ai. It would be the MAIN file. For example, in ZT2 there are xml ai files for BearGrizzly, then for BearGrizzly_F and BearGrizzly_M, etc. Their shelter is located in the main BearGrizzly. If I were editing something I would copy the line exactly from an animal who does use the shelter I wanted, and place it exactly where it shows in that animal's ai file. That is, if I were doing it for my own personal use.