Quote Originally Posted by Demon6324236 View Post
So far as I knew you can not have 2 items that have a Rare tag on them with the same name, in which case the simple solution is to call the lv90~99 version, Thief's Knife.
That would basically be an augmented Thief's Knife (a different item with the same name is probably even impossible), which has also been suggested, but there is currently no way to upgrade weapons this way. SE would have to invent an entirely new system just for that Thief's Knife, although they could potentially include other items as well, but it's still unlikely to happen. There has been a lot of discussion on it here.

I still say screw it, this is not on a list of worries at all. TH is a ridiculous argument for gameplay, in either direction. It's not something that should stand out in the first place, but a sidegrade to the job's other unique features, of which THF currently has close to none, and that's the real issue, not increasing the drop chance by a marginal amount.