Q: For a bulk upgrade of Windows RT devices to Windows RT 8.1, is there a way to perform this upgrade without using the Windows Store?

A: The only supported way to upgrade a Windows RT 8.0 machine to Windows RT 8.1 will be via the Windows Store. If you were willing to wipe the machines blank, then a Windows RT 8.1 USB Recovery Drive could be created and used to install other Windows RT devices. However, this would wipe the machine clean and you would lose everything.