So right now I'm a werewolf, and enjoying the perk tree for it. I'm also enjoying Hircine's Ring, which is letting me eat a dungeon of bandits, then loot them as a Naked Nord, sell everything, then go and eat another dungeon that same day. What I was wondering is when I become a Vampire as part of Dawnguard's questline, can I still use Hircine's Ring to become a werewolf, or does it just become a useless trinket? According to the Elder Scrolls Wiki (not UESP), the 1.3 and 1.4 patches enabled the ring's effect, so long as your character was once a werewolf.

But then, I've also gotten "iffy" information from the wiki, so I'm asking you guys. Also, my character is already wearing some Vampire Armor, and I want her eyes to match.

You should not be able to. Vampirism will remove lycanthropy.

I agree, it isn't possible by normal means. It would likely cause serious problems in the game if it was possible.

Do note us vampires have 2 rings to quest as well thru a radiant.