The page https://tracker.pureos.net/w/development/packaging_overview/ documents how to add a _higher_ number when forking from Debian.
Matthias clarified today on Matrix that "whatever works, as long as the string "pureos" with a version number suffix appears in there".
Please expand the guidelines to mention the existence of the "~" for Debian-based package versioning, used in situations where important to stay _below_ a certain other version.