We want to create a executable program which is either registered or unregistered. When unregistered we want to install an expire date which tells the user for how long he/she can use the program unregistered. However when the user decides to register the program we want to give the user some sort of code to install so that the program recognizes that the program is registered.

Does anyone have a clue or different kind of solution for this problem?

Thanks in advance.