I don't see any reason why not.
Your geese are not unique in their preference for grain. Grain is a concentrated source of calories, in nature those are hard to come by and so they're biologically programmed to like it a lot. In nature this would help them survive by making them likely to consume as much as possible whenever they found it. In domestic settings it's delivered daily and thus, it's the human's job to ration it out. Take the grain away, let them get hungry, they'll figure out the hay and then once they're eating it well you can start giving them a limited amount of grain again each day. You have to motivate them to eat it otherwise they will choose grain instead. The first couple days don't be surprised if they are reluctant and pitch a protest. Ours eat only grass and legumes they forage on their own throughout the entire growing season, no grain, they still protest when they first have to switch to hay in the winter. Takes them a day or three and then they figure it all out. They won't starve themselves so let them have their fit and get over it and then go about your business as usual. HTH!