When adding the "Editable Email Notifation" post-build action, the job URL page has a "Email Template Testing" link that allows us to select a template, and a respective build number to see what the generated email will look like.

It would be nice if a similar option was made available for the "Editable Email Notification Template" plugin.  This way, when we change the template, we don't have to trigger a new build to see the outcome.