After having trouble with Linux (openSUSE Leap 15) and Windows 7 overwriting each other's boot sectors (and me failing to integrate GRUB2 into Windows 7' boot menu), I wanted to put GRUB2 on a bootable CD (mostly trial and error due to poor documentation). I was able to boot Linux successfully with that CD.
However after a kernel update I noticed that the CD also contains the boot configuration file, so the kernel configured there does no longer exist on harddisk, and I'll have to edit the boot command line for the current kernel and initrd each time.
Is there a way (and how!) to put the complete GRUB2 on bootable CD while reading the actual GRUB configuration from harddisk? In my understanding a complete GRUB2 would have all the tools to read the Linux filesystem, so that should not be the problem, especially when the location of the boot configuration file does not change.