Thanks. It looks good. I'll try that.
In my case it's remotely controlled headless system so hopefully there will be possible ssh unlock on reboot.
Update: Almost forget to return back with result - yes, it works as expected.
Internet is full of easy to follow guides so just briefly:
1) Follow you favourite guide like
https://gist.github.com/XSystem252/d274cd0af836a72ff42d590d59647928 https://gist.github.com/devgioele/e897c341b8d1c18d58b44ffe21d72cf62) There ignore UBOOT and boot.txt related tasks
3) Because you'll swap the kernel:
https://archlinuxarm.org/forum/viewtopic.php?f=9&t=163604) Finally replace in /boot/cmdline.txt
$this->bbcode_second_pass_code('', 'root=/dev/mmcblk0p2')
by
$this->bbcode_second_pass_code('', 'ip=::::pi-locked:eth0:dhcp cryptdevice=UUID=>>PUT_YOUR_UUID_HERE<<:root root=/dev/mapper/root')