[Endoperez]

Items can't currently cast spells. However, weapon effects can include ranged elemental effects, close-range area-of-effect attacks and can have any existing special weapon ability like disease, paralyze, causing eye-loss, arm-loss, chest wound or crippling the target, etc. Far from perfect, though.

If you meant making an item cast a spell on the unit that wields it - not possible either. I don't remember if you can copy abilities of an existing item. If you can, you could replace special properties of any one item with those of any other, such as make a helmet that gives fire immunity like Ring of Fire, or make a shield that increases attack by 4 and morale by 2 like Ring of the Warrior.