We reviewed grml-rescueboot last month. But we have not reviewed how we preview the GRUB bootloader changes instantly without restart. With a tool called grub-emu, you can do it. It is not limited to grml, but every changes into GRUB configuration. It is useful for you when you often install another Linux distros or change any GRUB appearance. By using grub-emu, we will see a new window showing us exactly what GRUB will appear.
The package grub-emu is in official Ubuntu repository. Install it by command line:
sudo apt-get install grub-emu
In the Terminal, type command:
grub-emuTerminal will invoke a new window contains bootloader. That is what your GRUB will appear. Probably, you will need a few seconds until the GRUB appears completely. See picture below.