Yes. Players on Mordred and Gaheris can place any decoration or trophy from any realm in their houses. Items bought from your house's Store will always be of the same style as your character's realm of origin. For example, if you're a Briton, items bought from your house's store will always be of Albion design. In order to acquire a Midgard style decoration, you would need to purchase it from a markeplace in the Midgard housing zone.