It's possible to edit grub.cfg, but generally not advisable.
New menu entries are supposed to be added through custom scripts added to '/etc/grub.d/'
Some other settings can be changed in 'etc/default/grub'.
You are then supposed to run 'update-grub2' which automatically edits grub.cfg.
Why they are making this so complicated, I don't know.
But the syntax for the custom scripts is going to be a bit hairy for typical desktop end-users (it's actually a shell scrip).
Hopefully there will be a utility created to simplify this a bit.
For full explanation see:http://ubuntuforums.org/showthread.php?t=1195275