The current workflow is to duplicate the application, modify the duplicate and then republish. I think this is covered in the manual. It works pretty well but I'm assuming a more advanced workflow (perhaps involving version control?) is coming!
When I make the duplication I cannot modify the master metrics and dimensions. This means that I must know ahead of time ALL the possible metrics and dimensions that would be needed?
I agree with the workflow you describe above with one extra step... delete the original after the changes are made OR leave both versions... I would think this will lead to 100s of duplicated sheets with small changes being published.