If anyone else got the problem with reregistering account, it's because Mitakuuluu has a bug to save the new password in it's database. You can either wait till coderus fixes it, or fix it manually.

In /home/nemo/.whatsapp/ directory is a database called whatsapp.db. This one you need to update, either on device with sqlite3 binary or by copying to your PC and doing it there in a SQL editor.

You can see your new password in the whasapp.log file after trying to registering. It should look similar like this:

[D 16:13:37 SERVER] src/Whatsapp/warequest.cpp:95 void WARequest::readResult(): Reply: "{"status":"ok","login":"yourphonenumber","pw":"yo urnewlongpassword","type":"existing","expiration": 1551272944,"kind":"paid","price":"0,89 \u20ac","cost":"0.89","currency":"EUR","price_expi ration":1396965887}
"

As I'm not that strong with SQL syntax I copied the DB file to my PC and updated it there. The resulting syntax was:

UPDATE "main"."login" SET "password" = ?1 WHERE "rowid" = 1
Parameters:
param 1 (text): yournewlongpassword

After that I copied it back and set it to privileged group again:
chgrp privileged /home/nemo/.whatsapp/whatsapp.db

Make sure to close Mitakuuluu completely before trying to login with your new credentials:
killall harbour-mitakuuluu
killall harbour-mitakuuluu-server

Now start Mitakuuluu and have fun!


p.s. I'm not sure if this works also with totally new accounts where no database exists yet.