Update: It turns out it’s not my custom keybinding that made this work. Apparently it was already there and just happened to be bound to the same key I was experimenting with. You don’t need to do anything… the tip is really just that Command-Shift-Option-S already is the old Save As behavior. There, saved you some trouble!
If you do want to replace the S behavior with the old style, just make a Keyboard Shortcut for “Save As…” in System Preferences:
Quick tips are random posts regarding something I discovered on my way to something bigger. They usually get longer than “quick” would imply, for which I refuse to apologize.