Thanks jakibaki for your instructions!

One additional question: If I installed the community build, performed these countermeasures:
devel-su
mkdir ~/oem
mount /dev/disk/by-partlabel/oem ~/oem
rm -rf ~/oem/*
cp -ar /system/vendor/* ~/oem
umount ~/oem
rmdir ~/oem
then do I still have to use emma to return to the latest Android for XperiaX or can I just flash official downloaded SailfishX over the community build?