Another show that drew attention to the switching of actors to play the same character is "Due South". It's about a Mountie working in Chicago. At one point, the actor playing his Chicago Police Dept partner switched from a somewhat frumpy dark-haired man to a (in my opinion) very handsome but somewhat ragged blond guy. I forget exactly how they dealt with it -- the new guy went undercover as the old guy or something. But I think he was reluctant to do so, and couldn't figure out why everyone was calling him by the old character's name. I wish I could recall more -- I do remember laughing a LOT when I saw it.