No problem
I haven't had a dwarf hammy, but our Robo never empties his bowl - in fact it hardly seems to go down! And won't eat from it again unless there is new food! Maybe they vary
Anyway main thing is to reintroduce a new food gradually until it's changed over. The Bunny mix is very good too. You'd be better with either than the current Pets at Home one - I suggested the Burgess because it's easier to get hold of, but you could always order in bulk from Zooplus.