On calibre, you can tag a story anything you want. It helps for searching within calibre, but it does nothing once it's on the kindle device. No sorting, can't see the tags at all. So you can edit the tags in calibre as often as you want (including marking them read, a star system for your quality ratings, etc), but there's no syncing to kindle because they don't show up on kindle at all.
I still tag my stories because once you've got a bunch in calibre, it's useful for searching for something.
For keeping track of unread stories, I put everything new on my device in an "Unread" folder, then when I'm finished, I either move it to a permanent folder like "Science Fiction" or "Non Fiction" or I delete it, if I don't forsee re-reading it anytime.