Currently, the Release Template for Phases and Milestones only applies to new releases created and there is no way to apply a Release Template to an existing release, or to update an existing release with a new/updated Release Template. This would be extremely helpful, as we have created our release Road Map, but are still defining the Phases and Milestones for our processes.
Thank you for the idea!
It is now possible to apply a new release phase template to your existing releases from the menu in a release drawer.
You can select between:
Add to existing: keep all existing phases and milestones and add the ones from the new template
Delete and replace existing: Delete all existing phases and milestones and replace with the ones from the new template.