Remapping power and volume keys
Answering own question in case anybody else has the same issue.

There is another file /system/usr/keylayout/Generic.kl that contained the mapping for the power button. The Android docs say never to modify this file but I did anyway. Commenting out the power button line in this file has solved my issue (power button stuck in) and I'm now using my volume up button as the power button.

Note that I also had to remount the /system partition as read-write that I did with the excellent FX app