This is Bob, yes you can rename him. I don't think mimics really know they have a name anyway. I found Bob to be exceptionally good at hording all my gold. Conversely, he also made a good pickpocket, holding him near someones coin purse would result in his long tongue nicking it from the hardiest belt. Much more friendly than your average mimic, I found him to be a lovely companion and fiercely protective of me in a fight.