Kirk,
TN doesn't accept mailboxes for licenses and registration. We did a change of address a couple years ago and got them to accept it but last year they didn't want to renew my plates and finally agreed if I paid cash and said they may call me during the week to cancel my registration. So far they haven't. When the DW renewed her licenses last year the local office would not renew and sent it in to state to be to be reviewed, it was renewed but no star on the licenses.