I’m getting a new PC preinstalled with Windows 10 home. Can I still switch it to unlicensed Pro with default key 3V66T using slmgr or do I need to clean install Pro? I notice the message on activation screen in settings it says “You can no longer use Win 10 Default key to switch between editions until we verify you will be activated on the target edition. Except, if no reboot is needed you can use slmgr /ipk default key to switch” I’d test it but PC hasn’t arrived yet, all my current PC have digital licenses and I’d like to plan ahead
Where did you notice that message? And you can't switch license between Home and Pro, it will be an upgrade by key: https://forums.mydigitallife.net/th...20h1-2-vb_release.80763/page-157#post-1601562
From Home(sl) to Pro or higher is by settings and does a real online upgrade (Home<>SL is also an instant license switch by /ipk key), once on Pro or any of the other business SKUs it's an instant /ipk key license switch to switch to all other business SKUs.