hardware changes make identical grub boot into different OS

"Relabel the Fedora root partition. The bootloader is getting confused. Something like e2label /dev/hda3 /centos, then modify your GRUB entry (and possibly /etc/fstab) to point at that as the label.

Alternatively, you could relabel the Fedora root. Or take the easy way and point /etc/fstab and the root= directive in your menu.lst at /dev/hda3 rather than a filesystem label."