Say you find a +4 goblinoid bane rapier. Nice bonus, but you're not fighting goblinoids. Can you use crafting to remove the goblinoid bane special ability, in order to add on something more relevant (or at the very least, so you can just call your weapon a "+4 rapier" and save some syllables at the table)?
There are two main methods for "disenchanting" a magic item.
Both are rather permanent.
- Mordenkainen's Disjunction - This spell (known as Mage's Disjunction in the SRD) will completely disenchant (and destroy) one or more magic items and/or effects permanently.
- Artificer's 5th level Retain Essence class feature - This ability allows an artificer to 'deconstruct' a magic item, and recover some of the XP used in crafting it as Craft Reserve points. The item is destroyed.
In either case, you will need to make a new item from scratch, but at least with the Artificer's route, you'll recapture the XP needed to do so. Other methods are available to reduce the time and cost (and even auto-craft) the item you actually want.
Your DM may optionally allow a homebrew modification to the Artificer's Retain Essence class feature to permit it to target specific abilities instead of the whole item, which should not unbalance most campaigns, especially if the Artificer in question is an NPC.