I believe, but stand to be corrected, that the DH8-400 is a differences course and brief period of line training if already DH8 endorsed.
As for the -100, -200 & -300, the one endorsement certainly covered me, and that was with Mr CASA looking on too.
The downdide of using a DH8-400 across the Top End will be the 1500kg to 2000kg of freight, on top of baggage, that regularly goes under the floor of the DRW-GOV service.