If I recall correctly, you can even edit these "on the fly" with GnomeEditor (ie, you can change them even after starting the campaign). So you could theoretically start the game as say Duke of Normandy with Feudal Knights as your King's unit, and then change it to Royal Knights after conquering England?

Has anyone compiled a list (or can just tell me) which editable items must be changed before starting a campaign, and which can be changed after start?

For example, from what I saw before VI, you can still change Province & Capital/Castle names (in names.txt) after the campaign starts. The same is true of unit stats using GnomeEditor?