If you are a Windows user then you will be aware of Windows Product Id.A Product Id is a numeric value which is calculated according to the Activation keys entered by you to activate your Windows Copy.
You can check your Product Id by Right clicking My Computer => Properties, Or by pressing Windows Key + Pause/Break Key now a new window will be open and just navigate to the bottom and you will see your Product Id.
Now instead of that numeric value you can put any name which you want.See the belows screenshot:-
There may be several reason to alter your product key like for safety, to play prank with your friends etc.
So here we go:-
Open run command and type regedit, to open your Registry Entries
now navigate to:-
HKey_Local_MachineSoftwareMicrosoftWindows NTCurrent Version
Now on the right side pane you will see a entry name ProductID
Double click on it and you will see a box appears which contains your ProductID just copy your keys,you may need it in future,And replace that key with any name of your choice.
Thats It, Now go and check it
If in future you wanna roll back then just paste the key which you had copied.