Use kpasswd to rotate through a number of passwords between your old and new passwords

rotate-passwords.sh

#!/usr/bin/env bash

CYCLE=24
declare -a PASSWORDS
let last_cycle=CYCLE+1
PASSWORDS[0]=$1
PASSWORDS[${last_cycle}]=$2

for i in $(seq ${last_cycle}); do
  echo $i
  if [[ $i -ne $last_cycle ]]; then 
    password=$(pwgen -y -r \'\"'\{}$[]#;!' 10 1)
    PASSWORDS[${i}]=${password}
  else
    password=${PASSWORDS[${i}]}
  fi
  export NEW_PASSWORD=${password}
  let last_i=i-1
  export CURRENT_PASSWORD=${PASSWORDS[$last_i]}
  expect <<EOD
spawn kpasswd
expect {
  {Password: } {
    send "${CURRENT_PASSWORD}\r"
    exp_continue 
  }
  {New password: } {
    send "${NEW_PASSWORD}\r"
    exp_continue
  }
  {Success} {
    return 0
  }
  -re '.*' {
    return 1
  }
}
EOD

done