The commercial product likely is not the part specified in the approved aircraft drawings; does not come with certificates of conformance and the necessary traceability paperwork; and probably was not subjected to environmental stress testing, among other things.

Edit: unless they’re talking about the commercial aircraft part for the airline version of this plane (e.g. 767 parts for KC46). In that case, the parts are likely interchangeable and there should be some way to make the paperwork work.