The config will stay if you change the config/bmminer.conf
Cause config is on a seperate writeable space on the controller.

You could also do some coding there in one of the files which are executed every time
the miner restarts.

You could also change the ssh password by changing config/shadow
First change the password with passwd
then copy etc/shadow to config/shadow or just the first line with the root password

By the way this is a known security issue of antminers machines.
The default ssh root password.

cheers
and
MINE ON!!