OK. I have to say I do not understand what pianos intervenidos is. It is just in a translation, so I have no idea. In any case, what is the verb for architecture, for the element that you have to intervenir?
Are you talking about a "prepared piano?"
I would not apply the term "prepared" to any other artistic context, however.
Since your idea is very broad: the discipline of architecture itself-- any number of adjectives or phrases might express the idea of alteration, but to find a specific term, you would have to give us a more specific context: at the very least, a sentence in which this phrase might be used.