Az MS szerint bármikor visszarakhatod. :)
https://support.microsoft.com/hu-hu/help/12435/windows-10-upgrade-faq
Az OEMRETAIL viszont tényleg úgy van, azaz (szerintem) bármikor átrakhatod a retail előző verziót másik gépre de azt már nem fogod tudni upgradelni W10-re.
Bár a fene se tudja már őket követni:
Based on Insider feedback, we are also introducing the ability to link your Microsoft account (MSA) to the activation digital license with this Insider Preview build. If you already used an MSA to log in to your activated Windows 10 Home or Pro device, your MSA will be automatically linked. You can use this MSA linked digital license to re-activate your Genuine Windows 10 device by running the Activation troubleshooter, if you run into Activation issues caused by hardware changes.