Here is a summary of the information I found:
For Pixel and Stout we need to find the write protect jumper...
The rest is ready to flash from system!?
May 2012 Samsung Series 3 Chromebox Stumpy support yes: choose mainboard vendor samsung
May 2012 Samsung Series 5 550 Chromebook Lumpy support yes: choose mainboard vendor samsung
for finding the write-protect jumper of the 2 above look here: https://a77db9aa-a-7b23c8ea-s-sites.googlegroups.com/a/chromium.org/dev/chro...
a disassembly guide from chromium.org: http://www.chromium.org/chromium-os/developer-information-for-chrome-os-devi...
October 2012 Samsung ARM Chromebook Snow (aka Daisy)
needs a screw in to disable write protect https://a77db9aa-a-7b23c8ea-s-sites.googlegroups.com/a/chromium.org/dev/chro...
disassembly guide here: http://www.chromium.org/chromium-os/developer-information-for-chrome-os-devi...
November 2012 Acer C7 Chromebook Parrot
to find the write protect jumper look here: https://a77db9aa-a-7b23c8ea-s-sites.googlegroups.com/a/chromium.org/dev/chro...
the disassembly guide from chromium.org to get to the write protect jumper: http://www.chromium.org/chromium-os/developer-information-for-chrome-os-devi...
January 2013 Lenovo Thinkpad X131e Chromebook Stout
there is no information on chromium.org for disassembly guide see http://support.lenovo.com/en_US/downloads/detail.page?DocID=PD024821
February 2013 HP Pavilion 14 Chromebook Butterfly
to find the write protect jumper look here:
https://a77db9aa-a-7b23c8ea-s-sites.googlegroups.com/a/chromium.org/dev/chro...
disassembly guide on chromium.org http://www.chromium.org/chromium-os/developer-information-for-chrome-os-devi...
February 2013 Google Chromebook Pixel Link
no information about write protect jumper on chromium.org
disassembly guide:
http://www.chromium.org/chromium-os/developer-information-for-chrome-os-devi...