Flybe DHC8 pilots would initially fly both types and I believe sometimes on the same day. This only stopped when the classics were retired.
I was trained for the Q400 while flying the classics although oddly enough I never flew the 400 as I returned to the 146 fleet.
Out of interest I was also qualified for the RJ100 and had Flybe kept the 4 RJ100s they got from Turkish then I would have flown the 146 and the RJ100.