you can turn it off… quit rhino then using Terminal.app, enter this:
defaults write com.mcneel.rhinoceros ApplePersistence -bool no
that will disable autosave, bring SaveAs back to the file menu (instead of duplicate)… it also takes away the ability to add tags, rename, move via the window title (which i personally like a lot)
to change back to default behavior, enter the terminal command again but replace ‘no’ with ‘yes’
that said, i haven’t completely tested it so i’m not sure if other unforeseen behaviors will result… ymmv
[EDIT]
if you want to mess around testing it, i’d suggest making a copy of your current .plist prior to turning off ApplePersistence… restore your good .plist if something goes wrong…
outlined here: