You have to edit the scripts that generate /boot/grub/grub.cfg, not that file itself.
For the Ubuntu entry, check out /etc/grub.d/10_linux and search for the lines that output menuentry. The relevant part on my system looks like this:
echo "menuentry '$(echo "$title" | grub_quote)' ${CLASS} \$menuentry_id_option 'gnulinux-$version-$type-$boot_device_id' {" | sed "s/^/$submenu_indentation/"
else
echo "menuentry '$(echo "$os" | grub_quote)' ${CLASS} \$menuentry_id_option 'gnulinux-simple-$boot_device_id' {" | sed "s/^/$submenu_indentation/"
fi
I think the first of those (with echo "$title") should be used for all "Advanced options" whereas the second line (with echo "$os") seems to be responsible for the "normal" Ubuntu entry.
You can insert additional options in here, so that the correct menuentry line gets printed as you want it to appear in the grub.cfg file.
Don't forget to run sudo update-grub afterwards to regenerate the config from your changed scripts.
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