How to Downgrade Windows 7 Ultimate to Professional

Recently I had to install/downgrade one of my friend’s  Windows 7 Ultimate to Professional without format or data lose. I was thinking it could be straight forward and easy since both are same Operating Systems. But, that was not the scene. Ultimate version is the higher version in Windows 7 and it can’t be downgraded to  lower versions officially without formatting or doing a fresh installation. Anyhow, I found a trick to downgrade Windows 7 ultimate to Professional easily without new installation.
I’m not the owner of this trick, but I can confirm this works well.

Before start the installation, just change the two keys in Registry. Its like you are faking the Windows 7 installation that you are using the same version which you are going to install. In my case, I had to change the key to ‘ Windows 7 Professional ’. Make sure you are typing the exact and correct OS version which is written on your installation DVD

 

After you change the registry key, insert the Windows 7 Professional installation medium and start.
Make sure you have enough of space in ‘System Partition’ (usually C drive). Allocate enough of time since this will copy your personal data first, downgrade the OS and then copy back your data.
I suggest to clean up (move to different location) your personal data (such as Desktop, My Documents..etc) before start the downgrade for saving time.
Because of this method worked great for me and I managed to downgrade Windows 7 Ultimate to Professional, I recommend the original source with more details and screen shots.