Can you switch from a Non-ED visa directly to a Non-B visa in Thailand?

You can't change any Non-Immigrant type VISA to one of another type.

You MIGHT <- as in maybe be able to change an extension of stay of one type (like employment) to one of another type (like education)

BUT

I have only seen it a few times. most of the time you cancel your ED visa extension, leave the country and either get the Non-B visa from a thai consulate in another country OR come back on a 30 day visa exempt or a 60 day tourist visa and then apply for the 90 day Non-B at the immigration office.