I was trying to change the default Program Files install folder from an SSD to the hard drive last night and I think I ruined my Windows installation. I can’t run any exe. So, keep in mind that “Microsoft does not support changing the location of the Program Files folder by modifying the ProgramFilesDir registry value.” You’re probably best off just changing the drive letter for newly installed programs on a case by case basis. I always prefer to do stuff in the supported way.
UPDATE: I was able to run a command from the command line against a registry file that got me going again. It was a relief not to have to re-install Windows.