change ipv6 address of specified interface(not tested)

change_ipv6addr.py

#!/usr/bin/python
# -*- coding: utf-8 -*-
import subprocess
import binascii
import os

interface = "tap0"

## Get current ipv6 address
cmd = "ifconfig {0}|grep -e 'inet6.*global'|awk '{{print $2}}'"
cmd = cmd.format(interface)
addr_old = subprocess.check_output(cmd, shell=True).strip()
addr_prefix = ':'.join(addr_old.split(':')[:4]) + ':'

## Generate new ipv6 address
# get 4 * 16bit pseudo-random number by hex-string
byte2int = lambda n: int(binascii.hexlify(n), 16)
random_hex = ["{0:x}".format(byte2int(os.urandom(16 / 8)))
              for i in xrange(4)]

# make new ipv6 address
addr_new = addr_prefix + ':'.join(random_hex)

## Set new address and delete old one
# set
cmd = "ifconfig {0} add {1}/64".format(interface, addr_new)
print cmd
subprocess.call(cmd, shell=True)

# delete
cmd = "ifconfig {0} del {1}/64".format(interface, addr_old)
print cmd
subprocess.call(cmd, shell=True)