Script to change /etc/hosts and /etc/hostname if /boot/newhost is found

anewhost.sh

#! /bin/sh
### BEGIN INIT INFO
# Provides:          anewhost.sh
# Required-Start:
# Required-Stop:
# Should-Start:      
# Default-Start:     S
# Default-Stop:
# Short-Description: Changes /etc/hostname /etc/hosts if /boot/newhost found
# Description:       /boot/newhost file to change the
#                    /etc/hosts and /etc/hostname on start
### END INIT INFO

PATH=/sbin:/bin

. /lib/init/vars.sh
. /lib/lsb/init-functions

do_start () {
  if [ -f /boot/newhost ]
  then
    OLDHOST=`cat /etc/hostname`
    NEWHOST=`cat /boot/newhost`
    echo "Changing $OLDHOST to $NEWHOST..."
    echo $NEWHOST > /etc/hostname
    sed -i "s/127.0.1.1.*$OLDHOST/127.0.1.1\t$NEWHOST/g" /etc/hosts
    rm /boot/newhost
  fi
}

case "$1" in
  start|"")
    do_start
    ;;
  restart|reload|force-reload)
    echo "Error: argument '$1' not supported" >&2
    exit 3
    ;;
  stop)
    # No-op
    ;;
  *)
    echo "Usage: hostname.sh [start|stop]" >&2
    exit 3
    ;;
esac

:

Copy this script to /etc/init.d/ahostname.sh
sudo update-rc.d anewhost.sh start 01 S

If you create a new file /boot/newhost and put a hostname you want the RPi to become and then reboot, the anewhost.sh will change the /etc/hosts and /etc/hostname to match, remove the /boot/newhost file after the reboot.