As long as your itinirary contains a segment on LH group airline, the whole itinerary need to be flown as is and no parts of it can be changed.
This is because any change would require re-issuance of ticket and this can not be done anymore for itiniraries that include LH group segnents
You can cancel the whole itinirary and book the new one - but there is no guarantee that award seats from your previous itinirary will ge back into award pool, so plan accordingly.
Regards,
El Puerco Volante.