When you change the zoning to Comm, the residential mailbox will still be showing. Save the lot and exit to the hood. Then re-enter the lot. The Comm mailbox and trashcan should be showing when you enter the lot the second time. I save again just to be on the safe side, but the 2nd save may not even be necessary.
See, that just isn't happening in my game, with or without downloads/hacks. Problem was sort-of solved by deleting mailbox and purchasing comm phone/trashcan.