The only thing BTR would be a form/effect bonus, somehow, but if it's already a "dragon slaying" sword, I think you've already milked that one for all you're going to get.
For my money, I don't see a dedicated weapon being re-forgeable into anything but that- a weapon. Melting it down and making a "ring of unpleasantness vs dragons" just doesn't sound right. It's meant to be wielded as a weapon- possibly turned into a lancehead, or other such, but a cutting/impaling type weapon. (But that's a pretty subjective viewpoint, admittedly. Have to ask your GM. Or do (magical) research.)
Use it as-is, or see what sort of bonuses you could get to "reforge" it- which would be close to building one yourself, possibly. (But if the current bonuses are huge, it might be worthwhile to keep it as is, hence the suggestion for a spear-head etc.)
Edit:
As an afterthought, rather than having someone actually wield the weapon, IF you could piss it off enough, you could get it to charge you. If you had an effective T-port ready, even a short-range one, and had the weapon mounted as a "spear" behind you, you might get it to impale itself on the thing. If you were lucky.
But it would be less dangerous than going toe-to-toe with the weapon in hand.