I read over the documentation there. I'm sure it's safe to do, as you said you do it almost every day, but y'know, warnings in allcaps are worrying.
The warning (as you'll know) says that I'm asking grub to be installed to a partition rather than the MBR. Is there a way to install it "properly" to the MBR, or just update the MBR to look to /dev/sda8 rather than /dev/sda6?
e.g., The instructions for Reinstalling Grub, Method 2 on the Grub2 help page you linked show an example of using grub-setup, as opposed to grub-install, and says that the former command installs what's needed to the MBR as well as files to the partition. Might I be able to use it for my purposes? (with different arguments since I wouldn't be using a live cd, naturally)
What's weird is I read somewhere in the past half-hour that it grub-install can invoke grub-setup, so I would've thought grub-install would install to the MBR instead of throwing out threatening errors about installing to a partition...