this could be done, and for security, I'd recommend having the passwords in a text file that is on your computer, and nowhere else.
Code:
on *:connect:{
  if !%password_date {
    set %password_date $ctime
    set %pass_count 1
  }
  elseif $calc($ctime - %password_date) > 172800 {
    .msg nickserv identify <passwd>
    inc %pass_count
    if %pass_count > $lines(Password.txt) {
      set %pass_count 1
    }
    .msg nickserv passwd $read(Password.txt,n,%pass_count)
  }
}


There's probably better ways of doing this, but there's an example of how it could be done,