Q: Unix command to change admin password

passwd

https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/ man1/passwd.1.html

It's an interactive command.

You may consider dscl too, as explained at …

http://acletras.com/2008/04/30/force-local-user-account-password-change-through- apple-remote-desktop/

I don't know what OS version you are using so you will have to read the manual on your Mac to see if it applies…

man dscl

man passwd

Backup & test on a Mac you can afford to break before you automate it to multiple machines.

sudo -s dscl . -passwd /Users/USERNAME NEWPASSWORD && echo “Completed”

Replace the username and password, send as a UNIX command through ARD. It should feedback completed.