Earlier today, the B&W profile was sometimes appearing in the menus, sometimes not.
Now it seems to be staying! Strange.
Also:
In Document setup, I changed the Color format to Gray/8 and then selected the B&W profile.
In PDF Export, I set Colorspace to “As document” and color profile to “Use document profile”, and checked “embed profile”. In the resulting PDF, all the text added in Publisher was changed to 4-color.
When I un-checked “embed profile”, the text stayed 100% K.