- Download the ISO for the RP (from here)
- Mount the ISO as a drive (I used this)
- Attach the old VHD as a drive letter (Computer Mgt->Disk Mgt->Action->Attach VHD)
- Format the VHD drive to blow away the old Win8 CP
- Start PowerShell in Administrator mode to run the Install-WindowsImage.ps1 script (from here)
- Run Install-WindowsImage as shown below
- Assuming your boot menu Win8 entry is still in place, reboot into your new Win8 RP.
PS> .\Install-WindowsImage.ps1 –WIM D:\ISO\Sources\Install.wim –Apply –Index 1 –Destination D:\