This is mainly a placeholder for me so I don't forget this before the release.

Some possibilities:

• Alembic revision that just adds it in the database on the root category (plus code to store them during a new setup where alembic is not used)
• Store the templates as files somewhere in the indico package, and provide UI (on the category/event level) to "import" a default template

The second one is probably the cleanest option since it completely removes the need for upgrades etc. as users could just import the updated default.

Bonus option: Add a version number for the default templates and keep track on whether such template has been cloned from a default one, and show a "update to latest version" option if applicable.