More: Actually, if you accomplished your purpose I think your extensions should be showing, because it's default, but I don't know if you can toggle them off, because my experience has been that toggling that Finder pref only affects newly created items.
I toggle Finder > Preferences > Advanced > Show all filename extensions on and off regularly and it effects every file
regardless of when they were created*. The extensions are, always there, the only difference is whether or not Finder displays them.
Sorry, I rechecked and found that I didn't describe my experience quite correctly: a file created under "Show" retains its extension if I toggle to "Don't show", but I can toggle a file created under "Don't show" repeatedly. (I haven't tried in every OS version, but I first ran into that behavior in Jaguar.)
More: It just occurred to me to experiment, and I found that the behavior I described pertains to my desktop, but not Finder windows.
OK, it looks like the pref is NOT applicable to items in ~, but, for instance, .tiffs toggle in /Users/artie/Pictures while .jpgs and .pngs don't.
