- The mandatory user profile resets all user registry data upon each logon; so there’s no reason to use HKCU GPO keys (there are such keys).
- There are also HKLM GPO keys that LO reads; e.g. for Writer, it’s at
Software\Policies\LibreOffice\org.openoffice.Setup\Office\Factories\org.openoffice.Setup:Factory['com.sun.star.text.TextDocument']\ooSetupFactoryDefaultFilter. See more at Collabora ADMX. (However, it would be a funny setup to have mandatory profiles, and at the same time, permissions to write to HKLM.)
- Still, that is imo a really wrong thing. Even if you have a requirement to send something in a foreign format, it’s best to keep your data in application’s native format (ODF in case of LibreOffice), and only convert a copy to the foreign format when you are sending it. Otherwise, you are likely to run into situations where you loose some of the work, because of imperfect foreign format support, without possibility to restore it.
I’d say that if you still want to change your default save formats, then it’s better not to use GPO registry keys, but move your LO profile somewhere out of the mandatory profile tree, and run your LO with command line switch to point to it: