LibreOffice 4.2 introduced the ability to control LibreOffice settings via registry keys. In so doing, it allows Group Policy to set LibreOffice settings.
Unfortunately, LibreOffice have not provided much documentation on their main.xcd file, so it’s hard to know exactly what registry key you need to create in order to set a particular setting.
I have created a stub Group Policy admx / adml file for LibreOffice. Check it out on github.
With this admx file, hopefully it will be easy for you to set LibreOffice settings, without trying to figure out where the particular setting is stored in main.xcd.