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=1 will force registration of LibreOffice as default application for Microsoft Office formats;
• /msoreg=0 will suppress registration of LibreOffice as default application for Microsoft Office formats.

Source: http://www.libreoffice.org/get-help/system-requirements/