You need to be a root to do that, copy it back that is. The instructions here and elsewhere are confusing to me. I managed to gain root access by simply installing openssh, at some point they will ask you to define root password (that is password for user "root").

Then you can ssh from your PC (assuming that they both sit on the same router) to your tablet as user "root":
ssh root@192.x.x.x

where 192.x.x.x is your tablet local IP (good luck finding it!) and entering your root password.

For reasons unclear to me that password will not work in x-term on the tablet, that is
su
fails, and
sudo cp /media/mmc1/navit.xml /usr/share/navit/
will not accept your password.