Most of my island stays the same, but I have little things I'm changing up.
My surf shop next to the pier is now a hot cocoa & mulled cider stall. I'll keep it through the winter, although I'll tweak the colors.
In front of my RS, I have a little boardwalk with stalls for free DIYs, popcorn, cotton candy, and a drink machine. Those have been changed to autumn colors, as has the playground on the beach in front of it.
The shark spotting station now says the season is over.
I've swapped out my house exterior and the decorations in front of it for a fall look. I've also changed the interior to make it more cozy, although a lot of that was just changing the wallpaper and recustomizing furniture.