Ok, is there a way to go into a previously created mod and clear off all the cities and camps?

Your best option is to import everything you want to keep into a new file.
It's under File>Import

BTW, Welcome to CFC

In the editor under the Terrain tab. Select each terrain option and uncheck the box "Allow Cities". You can also remove resources and roads from the Terrain settings too.

I can't believe I never thought of that KA! I always did it the long painstaking way, thanks for the tip.