First post after a long time!
Registration of LibreOffice as default application for Microsoft Office formats can be forced or suppressed by using the following command line switches with the installer:
/msoreg=1will force registration of LibreOffice as default application for Microsoft Office formats;/msoreg=0will suppress registration of LibreOffice as default application for Microsoft Office formats.
Source: http://www.libreoffice.org/get-help/system-requirements/
