Will existing castles change to cities when I reform my government?

So, I'm playing as tribal Scandinavia and am nearing the point where I'll have to decide whether I want to reform to become a republic or a feudal state. I have already reformed the Germanic faith and am finishing up the last buildings in my tribal holdings. I'd like to form into a republic, since there are no formidable opponents (I am constantly beating France in Holy Wars).

However, I currently possess five "normal" castle holdings, of which four have cities as baronies. Will the castle holdings turn into city holdings, if I choose to reform into a republic?