You would need another tool. To push out new Splunk passwords, would need to, on each node, either:
./splunk edit user myuserid -password mynewpassword. Deployment Server can not easily be used to execute commands.
etc/auth/splunk.secret, and all other files that contain encrypts using
etc/auth/splunk.secretwhich usually includes just
etc/system/local/server.conf. These files much of course all match via
splunk.secret. Deployment Server can not be effectively used to distribute these files.
No, deployment server only pushes out App configurations, nothing to do with users, passwords or Splunk version updates. You might want to file an Enhancement Request if this is something you foresee a need for though.