I can turn off the sound for an NSNotify, but attempting to use this alternate sound is not changing the sound. The .aiff file is in the /System/Library/Sounds folder. (Other alternate sound files are not working as well.)
nsnotify “Sound: siubmarine?”,“Sound”,“Submarine.aiff”
Can someone confirm this please?
Yes, same behavior here.
It’s working for me if I leave off the file extension. If I include the extension, I just get the default sound.
nsnotify “Sound: siubmarine?”,“Sound”,“Submarine”Got it. I do see this noted in the upcoming Help files. 
There is an upside to understanding how those things work.