This is, in fact, possible:
- Boot the system using a linux live cd with
gdisk on it. I used a CentOS 7 Core installation and used recovery mode. I did this by editing the grub boot options and tacking on
rescue to the end.
gdisk on the disk with Windows installed. See the gdisk docs for more info.
- Reboot the machine into a Windows installation disk, and open up the command prompt using the
repair your computer option.
At this point, I had to load the VMWare PVSCSI drivers, and already had the floppy with the drivers mounted. To do this, you can run
drvload A:\AMD64\PVSCSI.INI. Alternatively, you can go through the initial Windows setup, and load the drivers via the GUI. You may then back out and click the
Repair your computer link.
Run the following commands to (with luck) restore the boot loader:
Note that your mileage may vary, and I would definitely at least snapshot the VM before doing this, but a full backup is better.