I recently committed to an Area51 proposal, and by mistake I selected "Professional or Expert" instead of "Academic or Research-Level Student" as my primary Role/Interest. Is there a way to change this, other than uncommitting and then re-committing?
There is no explicit way to change your "role" selection. Un-committing and then re-committing is the best way to make another selection.
There should be no side effects by doing this. Your commitment isn't "locked in" until the site gets created. Up until that point, you can change your committments around as you please.