An easy way to get a new manifest ID?

I'm about to "split" a existing app in two, and want to start with the same code base. I don't want to duplicate the manifest ID, as that can really confuse things on watches! So the ONLY thing I need to change to have a separate project is the manifest ID. (well, also the project name :) )

I can create a new CIQ protect and just grab that manifest ID, and then delete the dummy project, but I figured there had to be a different way to get a unique Manifest ID. Anyone know how to do that?