I think you have developer mode confused with the firmware write-protect switch. As far as I'm aware, every Chromebook has allowed enabling developer mode witho

I think you have developer mode confused with the firmware write-protect switch. As far as I'm aware, every Chromebook has allowed enabling developer mode without opening the device. Disabling the firmware write-protect (which does let you disable the ctrl-d requirement, and is what you need to do to install the UEFI firmware this guide refers to) used to require opening the device (to either remove a screw or flip a switch), but can now be done over CCD (closed case debugging) using the appropriate cable, as well as by opening the device.