The article Save slideshow settings as a slideshow collection talks about how to create a new slideshow and save it as a "slideshow collection". But if I later on make changes to that slideshow (change slideshow display options and/or change which photos are selected), are they automatically saved? There's no indication of auto-saving, that I see.
Yes, if you save a slideshow, changes made to it will be saved automatically, just as when you save a Print. If I remember correctly, the only change that is not saved automatically is Identy Plate.
So be careful if you want to try another design (without affecting the first). If you are still in the saved slideshow collection, you might lose your original layout (I know from experience). That's a good reason to always save the design as template in addition to saving the slideshow/print, so if you make that mistake you can reset the layout at any time 😉