Nice one, thanks for sharing.
That's my job for the weekend sorted.
Well done Galo!!!

OK.
To increase the dpi
create a file . Xdefaults inside ~/.local/share/libertine-container/user-data/container-name/
and set and set Xft.dpi:300 inside it .
cd ~/.local/share/libertine-container/user-data/container-name/ change container-name with your container name.
touch .Xdefaults
echo 'Xft.dpi:300' >> .Xdefaults
Libreoffice writer has a bug.
The first time you start the app, you can touch the menu items correctly. ( at least most of them )
After the second time you cannot access the menu and other functions correctly.
You may have to delete your profile always before start libreoffice writer.
cd .local/share/libertine-container/user-data/xenial/.config/libreoffice/4
rm -rf user
( xenial is the name of my container )
The calc and other libreoffice app are working correctly. ( for most icons ).
After changing the dpi, some icons will not work correctly because the position is changed, for example font color.
Good luck !