Jerome,
Since I rarely use ST High resolution, I forgot to test whether the Hatari OS X interface had been fixed to allow you to change to a monochrome monitor and reboot into ST High successfully.
Unfortunately, even with the released version of 1.7.0, you have to go into the SDL menu in order to change the Atari monitor successfully.
While I am posting this to the list, I know the developers will not be able to fix this since it is an OS X-specific problem. I was wondering if you found an obvious problem with the monitor change like you found with the Drive A and Drive B keyboard shortcuts.
I only ran into the problem today because I was trying out Word Writer ST and I wanted it in ST High resolution.
Bob C