There is already a long established science of this, in Systems Engineering, different layers of abstraction is how we term it, though I can't think if we ever used the term lumpability (If I come across an alternative, I will let you know!), I can't see anything wrong with it :)

Anyhow I see that as something different from Emergent Properties.

My understanding of what is meant by an emergent property is the emergence of intelligence, like we are seeing from positively powered LLMs, and we see in swarms of ants, and in the scourge of us on the planet, operating as we do for profit, which is fundamentally an energy lie, perhaps a necessary energy lie, to survive only on extracted energy (Mathematically negative energy) for a while, until we got to the technology of putting mathematically positive energy (Only solar) to use.

Actually I just remembered the term we use for "lumping together" concerns, we often call it "Bundling", so another variation on lumpability might be bundleability...