Regedit doesn’t allow to search for a string and replace it in any occurrence so here’s a quick workaround:
- open regedit and export required tree as a text (.reg) file
- search and replace in it using your favorite text editor (I suggest Notepad++ but notepad works) and save it
- import the file from within regedit
Note: if the keys you modified are in use you won’t be allowed to import them. If they are few you may want to replace them by hand, otherwise you might look for another specialized app.
As always, my final suggestion is: switch to a GNU/Linux distribution ASAP! 
