A very similar idea crossed my mind several times, but with a twist: altering LEGO CAD parts, but keeping the connectors the same.
Main idea was, if LEGO parts don't cover the needs for an agent to build a model, let it use the best it can find, and manufacture others if needed, but keeping same compatibility with the rest of the catalog.
And for that, instead of generating new parts from scratch, maybe mutating pre-existing parts into new shapes it needs, but leaving connectors as they were, or even adding new connectors but still compatible.
Main idea was, if LEGO parts don't cover the needs for an agent to build a model, let it use the best it can find, and manufacture others if needed, but keeping same compatibility with the rest of the catalog.
And for that, instead of generating new parts from scratch, maybe mutating pre-existing parts into new shapes it needs, but leaving connectors as they were, or even adding new connectors but still compatible.