to /etc/passwd and an SSH key to /etc/dropbear/authorized_keys. FYI, /etc/{passwd,dropbear/authorized_keys} will be overwritten. /etc/persistent/rc.poststart will be ...
you can enable a brute force solver for the proof-of-ownership challenge. This will reset the password to a OptString.new('USERNAME', [ true, 'The username to use for login', 'root' ]), OptString.new( ...