Energy Substitution( Complete Arcane, p. 79)
You can modify an energy-based spell to use another type of energy instead.
Knowledge (arcana) 5 ranks, any metamagic feat,
Choose one type of energy (acid, cold, electricity, or fire). You can then modify any spell with an energy descriptor to use the chosen type of energy instead. An energy substituted spell uses a spell slot of the spell's normal level. The spell's descriptor changes to the new energy type—for example, a fireball composed of cold energy is an evocation [cold] spell.
You can gain this feat multiple times, choosing a different type of energy each time.