Earlier this month, I didn't use Tiamo's replacement 32–bit bootloader to allow me to install OS X 10.9 Mavericks on my Mac Pro 1,1. At the end of that post, I said:

[..] there's no reason Apple couldn't change your lovingly replaced boot.efi with a future software update. You'd be wise to keep a bootable memory key with the altered boot.efi available in case you ever need to boot with it and swap it back.

With 10.9.2, this happened. Unsurprisingly, the solution is to overwrite the updated boot.efi files with Tiamo's replacements again.

Fixing in a nutshell

  1. Install the redistributable update, not the App Store update
  2. Before restarting, replace the updated boot.efi files
  3. Reboot

If you installed the update and now your Mac Pro can't boot (as I may or may not have done), you can replace the updated boot.efi files with your Mavericks boot key, or any other bootable Mac volume.

After booting, use the Terminal to replace these files with Tiamo's:

/Volumes/[Your Boot Drive]/System/Library/CoreServices/boot.efi
/Volumes/[Your Boot Drive]/usr/standalone/i386/boot.efi

If you get an error, you may need to unlock them first:

chflags -R nouchg boot.efi

And we end with another agreement that what you do to your machine is your own fault and responsibility. I didn't do this, and neither should you.