Then restore them, if still relevant, when uninstalling LibreOffice.

git log from build repository:
commit 1737ec9b6675cc7e30df03fa5537012a429425bb
Author: Tor Lillqvist <tlillqvist@novell.com>
Date:   Thu Oct 14 15:28:55 2010 +0300

    Make win32-restore-associations.diff apply again

commit 72a25ab4a055cd1d3cf5aec627cfe120113bfb34
Author: Tor Lillqvist <tlillqvist@novell.com>
Date:   Thu May 20 10:34:24 2010 +0300

    Make patches apply for a Windows build

commit d635f716a75d8c1648eab0c1d598b390be8c4f07
Author: Tor Lillqvist <tlillqvist@novell.com>
Date:   Thu Sep 17 22:16:40 2009 +0300

    Add new patch to restore MSO file associations on uninstall

    * patches/dev300/apply: Add it to Win32Only

    * patches/dev300/win32-restore-associations.diff: New file. Save
      previous associations of the MS Office file formats on installation
      of OOo. On uninstallation of OOo, restore them. Still a bit
      experimental, but seems to work.