I am going to recommend just telling software to install on the other drive. Most software lets you select it's install location
Messing with the registry for this is not always good as you have already seen.
there is a program called steam mover. While made for moving steam games, it may work with apps as well. May be worth a try to move some apps over that did not know how to install on another drive.
I have not tried it, but you can't hurt things any more at this point.http://www.traynier.com/software/steammover