If you are referring to what appears in “Computer Name” property then that is not configurable at all - you can’t change it unless you go on the OS and renamed the machine’s name to be whatever you want (and that is what will appear in BigFix console). For Windows it’s a bit limited on OS-level as they still have 16 character limitation but on Unix/Linux you can put whatever you want.
Otherwise, you can always create a custom property and write whatever logic you want…if you want you can do: if (computer name = "X") then ("X.domain.com") else if (computer name = "Y.domain2.com") then ("Y.domain3.com") else (computer name)