Remove the keyboard by
1) Remove the rubber plugs over the screw access holes. Note that there's one in the top centre of the backing within the product label. It elided me and made me wonder why it was so hard to pry off the keyboard. Luckily I didn't break anything.
2) Remove the screws. There are 9 of them phillips head (I don't know what size, but not overly tiny)
3) Using a plastic pry tool, work around and pry open the gap between the keyboard deck where it nestles into the main body/frame.
4) Carefully lift the keyboard up and to the left. You don't need to disconnect the keyboard to get at the screw, just set it aside.
[https://photos.google.com/photo/AF1QipOLtMtHef0Esl9LGJ-YrZFEJzU5I24OeUkCXXQ6|Image of motherboard with write protect screw bottom right.]
5) The write protect screw on mine (HP Chromebook 11 G4) is in the slot on the right with the contact pad divided into quarters. Remove.
Reassemble in reverse of disassembly.