Packer template that's supposed to, but doesn't sysprep.

BundleConfig.ps1

$EC2SettingsFile="C:\\Program Files\\Amazon\\Ec2ConfigService\\Settings\\BundleConfig.xml"
$xml = [xml](get-content $EC2SettingsFile)
$xmlElement = $xml.get_DocumentElement()

foreach ($element in $xmlElement.Property)
{
    if ($element.Name -eq "AutoSysprep")
    {
        $element.Value="Yes"
    }
}
$xml.Save($EC2SettingsFile)

EC2Config.ps1

# https://github.com/mefellows/windows-machine-factory-tutorial/blob/master/machine-factory/scripts/Ec2Config.ps1
write-output "Updating Ec2 Config..."
$EC2SettingsFile="C:\\Program Files\\Amazon\\Ec2ConfigService\\Settings\\Config.xml"
$xml = [xml](get-content $EC2SettingsFile)
$xmlElement = $xml.get_DocumentElement()
$xmlElementToModify = $xmlElement.Plugins

foreach ($element in $xmlElementToModify.Plugin)
{
    if ($element.name -eq "Ec2SetPassword")
    {
        $element.State="Enabled"
    }
    elseif ($element.name -eq "Ec2SetComputerName")
    {
        $element.State="Enabled"
    }
    elseif ($element.name -eq "Ec2HandleUserData")
    {
        $element.State="Enabled"
    }
}
$xml.Save($EC2SettingsFile)
write-output "Updated Ec2 Config."

packer.json

{
    "variables": {
        "dependency_s3_bucket_name": "",
        "aws_source_ami": "ami-1af6d779",
        "aws_instance_type": "t2.micro",
        "aws_instance_profile": "",
        "aws_vpc_id": "",
        "aws_subnet_id": "",
        "aws_region": "ap-southeast-2",
        "soe_version": "",
        "build_number": ""
    },
    "builders": [
        {
            "ami_name": "{{ user `soe_version` }}-{{ user `build_number` }}-ad-windows-soe-{{isotime | clean_ami_name}}",
            "ami_description": "Autobuild of Windows Server 2012 R2 AMI with Active Directory features installed. Build Number: {{ user `build_number` }}",
            "communicator": "winrm",
            "iam_instance_profile": "{{ user `aws_instance_profile` }}",
            "instance_type": "{{ user `aws_instance_type` }}",
            "region": "{{ user `aws_region` }}",
            "source_ami": "{{ user `aws_source_ami` }}",
            "type": "amazon-ebs",
            "user_data_file": "{{template_dir}}/scripts/user-data.ps1",
            "windows_password_timeout": "60m",
            "winrm_insecure": "true",
            "winrm_port": "5986",
            "winrm_use_ssl": "true",
            "winrm_username": "administrator",
            "vpc_id" : "{{ user `aws_vpc_id` }}",
            "subnet_id" : "{{ user `aws_subnet_id` }}",
            "run_tags": {
                "DependencyS3BucketName": "{{user `dependency_s3_bucket_name`}}",
                "BuildNumber": "{{user `build_number`}}"
            },
            "tags": {
                "BuildNumber": "{{user `build_number`}}",
                "BuildUUID": "{{user `build_uuid`}}"
            }
        }
    ],
    "provisioners": [
        {
            "type": "shell-local",
            "command": "aws s3 sync --region {{user `aws_region`}} {{template_dir}}/PSWindowsUpdate s3://{{user `dependency_s3_bucket_name`}}/windows_soe/PSWindowsUpdate"
        },
        {
            "type": "powershell",
            "scripts": [
                "{{template_dir}}/scripts/create-packer-user.ps1"
            ]
        },
        {
            "type": "powershell",
            "inline": ["winrm quickconfig -quiet"]
        },
        {
            "type": "windows-restart",
            "restart_timeout": "20m"
        },
        {
            "type": "powershell",
            "scripts": [
                "{{template_dir}}/scripts/dsc-adds.ps1",
                "{{template_dir}}/scripts/delete-packer-user.ps1",
                "{{template_dir}}/scripts/delete-packer-directory.ps1",
                "{{template_dir}}/scripts/Ec2Config.ps1",
                "{{template_dir}}/scripts/BundleConfig.ps1"
            ]
        }
    ]
}