How to change active boot partition of Windows 8.1 UEFI?

I've a 64 bit Windows 8.1 on GPT / UEFI and am trying to boot to another OS without a CD-ROM or external harddisk.

I've created a fresh partition (Z:) and copied Puppy Linux.iso over to it. However, I can't change the active partition to Z:. diskmgmt.msc's "Mark Partition as Active" is grayed out:

diskpart's active command also doesn't work:

 –§–  The selected disk is not a fixed MBR disk.

The ACTIVE command can only be used on fixed MBR disks.

I've also tried both EasyBCD and EasyUEFi, to no avail.

How can we change the boot partition and boot to another OS ?

Answer

It's possible, but not certain, that you'll be able to boot the image you copied using my rEFInd boot manager. You can test this without installing anything to your hard disk by downloading the USB flash drive or CD-R image, preparing a boot medium with it, and booting it. If you're lucky, you'll see one or more entries for the Linux kernel(s) and/or the EFI boot loader from the Puppy Linux image you copied to your hard disk, and selecting that image should boot the OS.

That said, installing an OS in this way is highly non-standard, and there are a number of reasons why using rEFInd might not help in your case. I'm not very familiar with Puppy Linux, so I can't say how you're supposed to install it to a hard disk. Skimming its main page, I get the impression that it's intended mainly for use on USB flash drives and CD-R media, although there is one passing reference to installing it to hard disks. If you want to run something from your hard disk, there's a good chance that another distribution would be a better choice.