Bytes 153-160 of the Code-500 ephemeris header should contain the central body of integration, and not the central body of the output ephemeris file. Bytes 1577-1584 contain the central body of the output ephemeris file.
This can be considered a low-priority item. The described behavior is what GTDS does, but the Code-500 ephemeris spec is poorly written for these items. I suspect that some applications may actually incorrectly use bytes 153-160 for the ephemeris central body. It may not be necessary to take action on this ticket unless a user reports a problem.