If a new version of Tuleap fixes a bug or add a new functionality in PDF templates styling, then everyone will have to 1) read the release note 2) manually adjust each of their own templates to match the update.
Before the PDF template usage is widespread, we should introduce the notion of "default style", aka a block of style that is readonly and subject to change by Tuleap releases. It does not completely remove the need for customers to check that their templates are still ok after a Tuleap release, but it should decrease the need and the size of adjustments.
This is actually needed to deactivate the automatic numbering for artidoc document that manages manually its own section numbering according to sections level (see story #41805).