If you have gotten yourself a Windows 7 trial of any edition and it is about to expire, but you need more time to use it for whatever reason, there is a cmd command that allows you to extend the trial by resetting the remaining number of days to the one it was in the beginning. This can only be done three times and will be disabled afterwards. To see how many days of your trial are left, right-click Computer and select Properties:
To extend the time to use the trial open a command prompt by running cmd via Run... and enter following:
The command is only working if the value of SkipRearm in the Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform Windows Registry key is set to 0.