Windows 7: Can I activate the trial version with a new key?

I have the trial version of Windows 7 64-bit installed. I have rearmed it 3 or 4 times already, each time gives me another 90 days. My question, which has probably already been asked, is this:

I just bought the Windows 7 Home Premium update family pack. I can install it on 3 computers. I just installed it on my laptop. Now, what I want to know is, if I can just change the CD key on the trial installation to the one from the update family pack and activate it forever like that, or do I have to do a clean install??? I believe the trial version is Windows 7 Ultimate and my upgrade is Windows 7 Home Premium.

Please excuse the stoopid question.

What is the trial version?
If you installed with a legal DVD, just use one of the keys. You can activate by phone.
Activate Windows 7 by Phone

If rearming extends the trial by 90 days every time, you are using the Enterprise version trial. You can check by typing winver in the Start button search box, then hitting Enter.

Enterprise trial cannot be activated with Home premium key, you'll need to do a clean install from the dvd you bought, then use your key.

There is a workaround to in-place Upgrade or Downgrade from your installed version.

You make two small changes in the Registry to trick the installer into thinking it is doing an (always allowed) Repair Install of the same version.

Browse to the Registry Keys shown below and Edit to read exactly HOMEPREMIUM for the EditionID, and Windows 7 HOMEPREMIUM for the ProductName.

click to enlarge

Then boot the Home Premium DVD, connect to internet to get latest updates into installer, choose Upgrade install, resolve any conflicts given. Afterwards insert the Product Key at Computer>Properties link to Activate.

Well, thanks gregrocker for the workaround, but after reading the first post saying I couldn't do it, I went ahead and did the clean install before I got your post. It's on my backup computer, so I didn't lose anything.

Thanks!!

You got a better install anyway. Let us know if there is anything else we can help you with.