How to use:

We need to unpack, customize and rebuild the debian images to have a fully automated installation

./unpack | creates the work environment from a debian-installer.iso
./install | copies custom grub config to the build environment
./build | builds the new installer debian-preseed.iso
./generate | runs the previous three commands to do everything, useful for updating the installer images

Customizing entries

edit the custom/boot/grub/grub.cfg

Change the menu entries

menuentry --hotkey=d 'Default' {
    set background_color=black
    linux    /install.amd/vmlinuz vga=788 --- quiet auto=true priority=critical preseed/url=https://github.url/preseedfile
    initrd   /install.amd/initrd.gz
}

For Ex.

menuentry --hotkey=d 'Default' {
    set background_color=black
    linux    /install.amd/vmlinuz vga=788 --- quiet auto=true priority=critical preseed/url=https://raw.githubusercontent.com/kylernocturnalnerd/preseed/master/preseeds/default.cfg
    initrd   /install.amd/initrd.gz
}

Preseed Files

All go inside the preseed folder Can make as many as you like for different things

For ex.

./preseed/default.cfg - This preseed was given the above grub menu entry but I can create a second:

./preseed/with-vim.cfg - That contains an installer that auto installs vim then create another entry:

menuentry --hotkey=v 'vim' {
    set background_color=black
    linux    /install.amd/vmlinuz vga=788 --- quiet auto=true priority=critical preseed/url=https://raw.githubusercontent.com/kylernocturnalnerd/preseed/master/preseeds/with-vim.cfg
    initrd   /install.amd/initrd.gz
}