Thanks Jean-François, Unfortunately this is not enough as the non-Free file has to be removed too from the source package.
You can achieve this stably over upstream updates using uscan and the Files-Excluded field of debian/copyright. https://manpages.debian.org/unstable/devscripts/uscan.1.en.html#COPYRIGHT_FILE_EXAMPLES It might be useful to consult with the Release team to see if a Stable update is needed or not... Have a nice day, Charles
