https://seafile.nigle.nl/d/62d505f0a7/

Grab rootfs (ubuntu-xxxx.tar.xz) and device-xxxx.tar.xz from http://system-image.ubports.com with:

ubuntu-device-flash -v --server=http://system-image.ubports.com  touch --channel=ubuntu-touch/devel_rc-proposed –device=FP2 --download-only

Modify a copy of rootstock-device-install to use the parts of device-xxxx.tax.zx we need.
rename to rootstock-FP2-install

Boot to fastboot mode with by pressing volume down and power button till Fairphone logo comes up. Connect to USB cable
Check for fastboot mode.

sudo fastboot devices

sudo fastboot flash boot boot.img
sudo fastboot reboot-bootloader
sudo fastboot flash recovery recovery.img

Manually boot into recovery with up-volume button and power button.

use modified rootstock-FP2-install to install rootfs, system.img, and custom.tar.zx

Boot phone to Ubuntu Touch.
Set security.
Unset auto updates.
Verify adb
Set up /home/phablet/.ssh
run

phablet-config writable-image

To make rootfs writable.

adb shell

sudo add-apt-repository ppa:peat-new/fp2-custom-test
sudo apt-get update
sudo apt-get upgrade
sudo install xterm xauth mir-android-diagnostics mir-test-tools mir-demos synaptic

Test mir, etc.