BoED allows for the redemtion of evil magic items but doesn't touch on intelligent ones. In such a case, it's like crafting a new item but the evil one acts in place of the gold. If it is simply a magical construct, the I suspect that it could be redeemed in the same way. It does say that certain items are irredeemable and can only be destroyed. These are mostly artifacts and relics.
Typically, flavor text in the campaigns I've been in have said that intelligent items are made so by transfering a soul or spirit into them. First judge by the personality of said weapon if it can be redeemed or not. If it can't, then it can't and can only be destroyed. If redemption is a possibility, then I'd say that it would take some active event to redeem it. Simply putting it in a good space probably wouldn't do it unless such a space would also do the same to a living creature. Even then I'd consider it harder than changing the alignment of a living creature as it's nature is probably set with magic. I'd say that it would take effort on the PCs side to role play with said item, find out why it is like it currently is, it's personality, and then take steps to correct these or show it the error of its ways by playing up to other bits of its personality. Sort of like getting Darth Vader to side against the emperor, you'd have to figure out which buttons to push and then push them hard. Then, for dramatic reasons, in an epiphany, the item would change alignment and possibly change or gain new good powers that would save the day at the most desparate time.
Another point, is that if you could get an itelligent item to change its alignment, then maybe it would lose what ever powers it had. It might still be able to use them but doing so would mean reverting back to the old alignment which the weapon would not want to do. Thus an intelligent Nine Lives Stealer who has turned good would still have the ability to steal lifes but would/could not use the power unless it was to change back to its evil alignment , a choice the sword would have to make.
