I have had a PC with multiple versions of Ubuntu on it for a while using grub legacy to boot from a separate boot partition the version of Ubuntu that I wanted. When a new version of Ubuntu came along I created a new partition (using LVM2) and installed the new version of Ubuntu on it. When I booted a particular version and there was an OS upgrade the installation would ask what I wanted to do with menu.lst, I would do a three way merge, and the upgrade would complete, without changing the other OS's additions to the boot up menu.
How does this work with grub2 where the way of editing the menu is via a directory structure on OS's partition? Or is there a way of putting the configuration directory on the boot partition so that it can be shared by the multiple OSs that boot from it, and during an upgrade want to manipulate it? Or even if I want to add something, I don't want to have to make the same change to every OS's grup config dir.