From our trials with 6.0, we don't think the design is promoted and you need to a different tool to update the properties cq:template and jcr:resourceType of the jcr:content nodes below the nt:Page nodes, right Adobe Staff? However, 6.1 has gotten the "Ability to select which template to use when creating a new launch.".
With 6.0 the ACS tool "CVS Resource Type Updater" appears to be designed to replace templates, but "ACS AEM Tools is ONLY for use on development and QA environments.". You will probably need to promote the launch too, if you also changed pages.
To keep your production and development pages in sync, you should select the live-copy feature when you create the launch, I guess.
If you create a new live-copy launch immediately before the promotion of the launch with the new template, you still edit either the original pages or edit the new production version and let the changes be propagated to the original.