Changing the default installation directory in Windows 7 through registry changes

I said exactly what you said, but you are disagreeing with it...

1) Backup your existing directory (for posterity)
2) Reinstall to a new location
3) restore your backup without overwriting (unless you use an installer for an older version)

I have done this many, many times and it works like a charm.

ah, must have misread what you wrote. Cheers~