How do I change Spellcaster Type in an Archetype?

[bertraze]

I'm trying to replicate the Expempresario archetype for magi from Wayfinder Magazine #7, and I'm having a bit of a hard time with it.

The major change is that the Extempresario is a spontaneous caster rather than a prepared caster. There doesn't appear to be an override field for the Spellcaster Type on the Archetype tab.

I've also tried to use an eval script to replace CasterType.MemBook with CasterType.SpontKnow, but I always get an unspecified error when trying to compile my script.

I'm really puzzled on how to accomplish this without any software enhancements. Does anybody know what my script is missing?