Later installations typically allow the flight ID to be typed into the FMS. Some which originally didn't include Mode S have a separate way of "dialling" it in at the transponder.
I think in virtually all cases the ADS-B data is directly derieved off the Mode S data, so I don't think you will find aircraft with a seperate means to define it.
ADS-B is a subset ("extended squitter") of Mode S anyway.