Thanks for replying LaithArkham.
I am aware of the mod's existence, however it supposedly conflicts with some other mods. I was was under the impression that if it was included in the vanilla game wouldn't conflict with other mods. (or so I hope) Which is why I am interested in finding out whether the GOG version has it or not.
I guess I'll find out when it is released tomorrow.
Edit: I just found out that the ferret pet is also included in another mod
which adds 39 pets and supports 18 custom classes, which pretty much solves the problem the other mod had.