Possible, yes. Unity Editor is scriptable in theory. But it does only work if all your models are uniform and made in the exact same way. That's unlikely for stuff you "downloaded" somewhere. Stuff you can get for free is almost always broken in one way or another and need manual fixing of materials, scaling issues or root transform. Scripting only makes sense, if you got 1000+ things that all need to be treated exactly the same way. If its less than that you are likely faster doing it by hand.