Minecraft Java Edition – Can Command-Q Be Disabled on a Mac?

No, this is not possible in an un-modded, single-player game. There's certainly nothing you can do to a map file to force constraints on the player playing it.

Given that people have been playing adventure maps for ages without the special mode, trust has worked very effectively up to this point :-)

Most fullscreen programs on Mac OS 10.8 will use the four-finger swipe to switch between it and the desktop, but Minecraft doesn't obey this protocol. It appears to use a borderless window the size of the desktop instead of creating and using a separate fullscreen space. It also appears to set itself to be always on top, so Minecraft won't relinquish focus when you use ⌘+tab.

The only way I've found to quickly switch is, as you have, to turn off fullscreen. Fortunately, there is a faster way to do this: F11 is bound to the "toggle fullscreen" function. If you're using a laptop then F11 probably defaults to adjusting your volume or similar, and you'll need to use fn+F11 instead. The fn key is usually located in the bottom-left, under shift.