Energy Substitution( Tome and Blood: A Guidebook to Wizards and Sorcerers, p. 40)
You can modify a spell that uses one type of energy to use another type of energy.
Knowledge (arcana) 5 ranks, Any other metamagic feat,
Energy Admixture (TB) ,
Choose one type of energy: acid, cold, electricity, fire, or sonic. You can modify a spell with an energy designator to use the chosen type of energy instead. A substituted spell works normally in all respects except the type of damage dealt (see sidebar). A substituted 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 it applies to a different type of energy.