If itachi wants naruto to bring back sasuke i dont think he would give him such weapons. However he does love sasuke and would want to protect him therefore its possible that he gave him these weapons, however not the way you think via eye transplant. Wd just have to wait and see, but yes i agree, those weapons being wielded by a perfect susano is op, but also those weapons being wielded by somebody like itachi or sasuke and not their susano would also cause havoc.
[/B]
I get what you are saying. Changing properties is very vague and thats why i dont want to get into shape manipulation, because its only this word and no physical form do we have to back this idea. At the highlighted part, im no fortune teller. However i believe itachi found it in original form, by that i mean able to be wielded by a human. When he did attached it to susano might it have changed its size to allow susano to wield it. A shield is usually circle although it can be rectangular.