Energy Affinity( Miniatures Handbook, p. 25)
You can modify a spell that uses one type of energy to use another type (acid, cold, electricity, or fire) instead.
Knowledge (arcana) 5 ranks, able to cast at least one spell of each of these energy types: acid, and fire, cold, electricity,
Sudden Energy Affinity (MH) ,
Choose acid, cold, electricity, or fire. You can modify any spell with an energy descriptor to use the chosen type of energy instead. A spell so modified works normally in all respects except the type of damage dealt. A modified spell uses a spell slot of the spell's normal level, modified by any other metamagic feats.
You can gain this feat multiple times. Each time you take the feat, it applies to a different type of energy