This preflight script will do two things, 1) Set ClientIdentifer and 2) Block Updates, if applicable

preflight

#!/usr/bin/python
#encoding=utf-8

#######################################################################################################
# This preflight script will do two things, 1) Set ClientIdentifer and 2) Block Updates, if applicable
#
# ClientIdenfier is set to mac_address_en0.plist, (eg. ab:ab:ab:ab:ab.plist)
#
# This preflight script will Block Updates during the specified time, as long it is in `auto` mode and
# the current time is int the appropriate range.  Set the range, by setting the following keys in
# the /Library/Preferences/ManagedInstalls.plist file
#
#   BlockUpdateStartTime - set to the start time in military, (e.g. "08:00")
#
#   BlockUpdateEndTime   - set to the end time in military, (e.g. "18:00")
#
#   BlockUpdateDays - set to days the block should take effect, defaults to all days. You can NOT set
#                   the value or set it to "All".  If you would only like a specific set of days, define#
#                   define the value in a string like "0, 3, 5" to only block on Mon, Wed, Fri.
#                   0 is Monday, 7 is Sunday
#
#######################################################################################################

import os, sys, time, commands, datetime
from dateutil.parser import parse

from munkilib import munkicommon

def set_client_identifier(ci):
    """set ClientIdentifier based on MAC Address"""
    munkicommon.set_pref("ClientIdentifier", ci)

def get_mac_address(iface):
    """docstring for get_mac_address"""
    val = os.popen("ifconfig %s | awk '/ether/ {print $2}'" % iface).read().rstrip()
    val += '.plist'
    return val

def parseTimePref(pref):
    prefValue = munkicommon.pref(pref)
    if prefValue:
        return parse(prefValue)
    else:
        return ''

def current_day():
    """Return the day of the week as an integer, where Monday is 0 and Sunday is 6."""
    return datetime.datetime.localtime().weekday()

def current_time():
    """Return the current time in military format"""
    return 

def should_block_updates():
    if (in_blocked_mode() and in_blocked_day() and in_blocked_time()):
        return True
    else:
        return False

def in_blocked_mode():
    runMode = sys.argv[1]
    print runMode
    if (runMode == 'auto'):
        print 'in auto mode'
        return True
    else:
        return False

def in_blocked_time():
    startTime = parseTimePref('BlockUpdateStartTime')
    endTime = parseTimePref('BlockUpdateEndTime')
    timeNow = parse(commands.getoutput("date"))
    timeNow = timeNow.replace(tzinfo = None) # Strip the timezone info

    if (startTime and endTime) and (startTime <= timeNow) and (timeNow <= endTime):
        return True
    else:
        return False

def in_blocked_day():
    blockedUpdateDays = munkicommon.pref('BlockUpdateDays')
    todayNum = time.strftime('%w')
    
    if (blockedUpdateDays == None) or (blockedUpdateDays == 'All') or (blockedUpdateDays == ''):
        return True
    else:
        blockedDays = [day.strip() for day in blockedUpdateDays.split(',')]
        return todayNum in blockedDays

# Set Client Identifier
mac_address = get_mac_address('en0')
set_client_identifier(mac_address)

# Should we block updates or continue on?
if should_block_updates():
    print 'Updates have been blocked at this time.'
    sys.exit(1)
else:
    print 'Updates will continue at this time.'
    sys.exit(0)