I have a ball of smoked mozzerella that is 3 days past its date, but unopened. Can I still use it?

Should be no problem. The smoking process is intended to make it taste interesting but also hold longer. In Italy an equivalent cheese would be scamorza. It's a low moisture cheese so it doesn't have to be consumed immediately.

3 days past its "sell by" date or "use by" date? Regardless, since it's smoked and it's cheese, it's probably fine. I'd use it. Just check it carefully for any signs of mold or decay--strange coloring or strange odors.

Unless it looks or smells bad I'd totally eat it.