Can I use this amulet's power to spontaneously cast a spell modified by metamagic?
(Like converting an Icestorm into a selective Fireball or something similar.)
I personally don't see anyting in the rules gainst it, though it would proabably come with the usual increase in casting time of spontaneously cast metamagic spells.
I can see this being allowed if you have all the requisite feats or magical items to cast the metmagicked spell normally.
Indeed, this is pretty much exactly how Spell SPecialization works for a Blaster Caster build, you're just using a magic item instead of a feat.
==Aelryinth
Hmm. Similar question of Clerics spontaneously casting a Cure/Inflict spell with metamagic. Assuming the cleric had the feats to do so. Can it be done? (i.e. An Evil Cleric converting a Bestow Curse into a Reach Inflict Moderate Wounds)
It can already be done passively with the healing domain's ability to Empower all Cure spells.
Don't see any difference with doing it actively, if you have the right feats and/or gear.
==Aelryinth
Well, that domain empowers all Cure spells cast by the cleric, no matter how the casting was done. Spontaneously or not.
I don't really see the harm in this sort of spell maneuver, as Metamagic is often weaker than the spells of the level it would normally occupy.