Manually handling this by giving each theme a unique name, but my initial plan was to create a song, scripture, and presentation theme for each sermon series and title them all the same. On export, no errors or notifications when there's an existing theme with the same name. (First export was fine, but when I exported the second, I overwrote the first, and overwrote THAT one when I exported the third. Didn't know it was happening, and managed to thoroughly confuse the user who was importing the theme files and building the schedules.)

Having multiple, different, themes, all having the same name is a recipe for chaos and confusion...