Necromancer's Athame

This pallid length of sharpened thighbone is carved into the shape of a dagger, but with tiny holes bored into it at equal intervals, almost like a flute. A necromancer who selects the athame as his bonded object can use it to spontaneously convert any prepared wizard necromancy spell into any other wizard necromancy spell he knows; the desired spell must be of the same level or lower than the prepared spell.