I had this one dragon named Haborym that wound up being a recurring adversary for the region across two campaigns. The players christened him, rather unimaginatively, as Emberwing. Pretty sure that name was from Dragonlance.
Don't tell the players how. Let them come up with all the hoops to jump through themselves. Just see how long you can string them along with promises that "it's possible", or "it's having an effect". An alignment change on what sounds more like an artifact than an enchanted weapon should take time and be gradual. Like having it develop a bond with a player then have that player sacrifice (or near as makes no difference) himself in order to save it. There should be no procedural way to do it since it is intelligent.