Although it appears there is another way to make that, just for LXDE, using file /etc/xdg/lxde-mimeapps.list. May be it will be the best way after all.
- Bug#1005818: task-lxde-desktop: libreoffice is used as de... Andreas Tille
- Bug#1005818: task-lxde-desktop: libreoffice is used ... Andriy Grytsenko
- Bug#1005818: task-lxde-desktop: libreoffice is used ... Andriy Grytsenko