I'm trying to build a spell based on Ceresa's Corruption, except instead of changing any friendly shard to a Death Shard, it randomly changes the shard into a Death or a Fire Shard. However, I don't want a player to be able to circumvent the randomness by simply casting the spell again until they get the shard they want, so Corruption's "<SpellTargetType>RegularShard</SpellTargetType>" is too broad.
So, is there any way that I could restrict the target to Water/Earth/Life/Air shards only? I hoped to do this by adding a new <SpellTargetType> (i.e. "NotFireOrDeathShard"), but I can't find any xml that would let me add custom target types. Alternatively, is there a way to check to see what the shard is when the spell is cast, and only change it if it isn't a Death/Fire shard? If no, are there any other clever ideas out there on how I might pull this restriction off?