Hatteberg was a highly productive offensive player at first base, and improved his defense enough to field his position competently. I just mentioned him as a precedent for a catcher moving to 1st base successfully, though of course the circumstances were different. Hatteberg's career was essentially finished as a catcher, it took Beane's vision to salvage the OBP by converting him.
I don't understand why the Nats would want to change his position.