Switch Visual Studio 2010 License keys
Change the serial number after Visual Studio 2010 installation
Go to Control Panel -> Programs and Features, locate and highlight Microsoft Visual Studio 2010 Ultimate/Premium/Professional installation, and click on Uninstall/Change button.
Upgrade Visual Studio 2010 Product Key for Activation
A Visual Studio setup maintenance screen should be shown. After clicking Next button, an option to enter a valid serial number to upgrade product license is available.
Enter the upgrade key accordingly, and click on Activate button. No re-installation required.
There is a way to edit the product key in a file called Setup.SDB. It should be located in
\Program Files (x86)\Microsoft Visual Studio 10.0\Microsoft Visual Studio 2010 Professional - ENU\Setup.SDB
Edit this file in a notepad and search for Product key. You can then update the product key.
I actually repaired the installation after this change just to make sure everything was working. This was tested on VS2008 and VS2010