Enhance Effect( Player's Guide to FaerÃ»n, p. 135)
You can change the characteristics of a persistent spell effect that is already in place.
You can change any variables of a persistent spell effect that is already in place (except its point of origin or the spell's center of effect) as if you were casting the spell yourself, even if you can't normally cast that spell. For example, you can change the radius of a ring-shaped wall of fi re, but you cannot change its point of origin. You can substitute your own caster level for the spell's original caster level if you choose. You can also shape the effect as you desire within the parameters of the spell. As with the metamagic effect ability, you must be adjacent to or within the spell effect and make a Spellcraft check--in this case against a DC equal to 30 + (3 Ã— the spell's level). You can use this ability and your metamagic effect ability a total number of times per day equal to 5 + your Intelligence modifi er. Like metamagic effect, using this ability is a full-round action that provokes attacks of opportunity.