(Some people think of this as an upgrade!)
The ProCustom Group provides customization services for Getac laptop, notebook and tablet operating system with a customization downgrade from Windows 8 to Windows 7.
From the official Microsoft Website, the following provides more details about downgrade rights for Windows 8.1 Pro; Windows 7 Professional and Windows 7 Ultimate. Downgrade and down-edition rights are an end-user right that Microsoft offers to customers for certain OEM products which meet the technical requirements for a Windows software downgrade. Downgrade rights are documented in the Software License Terms that customers accept upon first running Windows and Windows Server software. Thanks to downgrade rights, end users who have acquired a later version of the software (such as Windows 8.1 Pro or Windows Server 2012 R2 Standard) can use an earlier version of the software (such as Windows 7 Professional or Windows Server 2008 R2 Standard) until they are ready to migrate to a later version technology.
If a product includes downgrade rights, the license terms for that product will indicate which earlier versions of the software may be used.