The only way you get to choose a name of an NPC is through making a custom NPC, and only those types. Not builders, or riflemen etc. As for the avatar, your own unique image can be applied using CPs on the Exchange CP page. There used to be a way to switch the avatar around through the default ones through that Edit NPC link. However that was broken, and hasn't been fixed yet.
Pretty much kills them off (don't get anything back from firing them, only if you sold them to the market, but you can't do that with NPCs so if you want to get anything for them then list them for sale, won't really get anything for builders/workers as most people don't even bother going back and picking them up when they have finished working)