Consider a spell with possible casting requisites - say, a MuCo(An) spell to change a human into a hog, where a Terram casting requisite will allow the caster to change the the target's metal armor and weapons as well. What happens when instilling the same effect into an item? I'd rule that if the creator accepts to be limited by the lowest of Animal and Corpus AND Terram, he can design an item that will change the target's metal (and stone) accoutrements; otherwise only Animal (and Corpus - YKES!) belongings change along with the target. But is there anything in the RAW about this issue?
Agree with your reading. The effect is built into the item and the creator pays the panalty.