I am not a programmer, nor pretend to be or know one. That being said, I wonder if one of the talented addon makers here could create an addon that would help with guild member ID. In my guild, there are about 20 regular players with several toons each. And every now and then, a new toon pops up in the guild that most of us can't identify until they tell us who they are. If there were an addon that could import my guild member list from the server, allow me to delete inactives, and let me assign a name to each toon as I choose, then display it next to their name in my guild chat, life would be better. I have seen a few identity adds for guild, but they all use the guild master's notes as their cues. I would like to assign my own nickname to each guild member's toon.
Well, Prat has an alias function. It's not quite as user friendly as you've described, you just give it a nickname for alts one at a time, but once it's set, it works real slick. Plus, Prat is an extraordinarily convenient mod in my opinion anyways, I'd recommend it in a heartbeat to anyone. It maybe be a little more bloated than you need, but that's my only suggestion. Sorry.
Ive been using Guild Greet and now Guild Greet - Extended (Available from Curse.com) for years now. I love it! It helps me keep track of who is who in my ever growing guild, as well as all the special features you can use, or choose not to. Take a look, it might be what you need. Happy Gaming^.^