Sample Packer template for ESXi 6.0 or 6.5 and vCenter 6.5 that shows the entries uuid.bios and vc.uuid diseappearing from the .vmx file around the time the builder "vmware-iso" ends and the post processor "vsphere-template" starts, then reappear with different values some seconds later (10-15 in our case depending on hardware speed)

packer.json

{
  "builders": [
    {
      "type": "vmware-iso",

      "remote_type": "esx5",
      "remote_host": "{{user `esxi_host`}}",
      "remote_username": "{{user `esxi_username`}}",
      "remote_password": "{{user `esxi_password`}}",
      "remote_datastore": "{{user `esxi_datastore`}}",
      "keep_registered": "true",
      "skip_export": "true",

      "output_directory": "{{user `vcenter_template_name`}}",
      "vm_name": "{{user `vcenter_template_name`}}",
      "vmdk_name": "{{user `vcenter_template_name`}}",
      "iso_url": "http://mirror.cisp.com/CentOS/7.4.1708/isos/x86_64/CentOS-7-x86_64-Minimal-1708.iso",
      "iso_checksum_type": "sha1",
      "iso_checksum": "aae20c8052a55cf179af88d9dd35f1a889cd5773",
      "guest_os_type": "centos-64",
      "communicator": "ssh",
      "ssh_username": "root",
      "ssh_password": "aPassword",
      "disk_size": 16384,
      "floppy_files": [
        "packer-ks.cfg"
      ],
      "boot_command": [ "<up><tab> inst.text inst.ks=hd:fd0:/packer-ks.cfg <enter><wait>" ],
      "boot_wait": "20s",
      "vmx_data": {
        "memsize": "2048",
        "ethernet0.networkName": "VM Network"
      },
      "shutdown_command": "shutdown --poweroff now",
      "vnc_disable_password": "true"
    }
  ],

  "provisioners": [
  ],

  "post-processors": [
    {
      "type": "vsphere-template",
      "host": "{{user `vcenter_host`}}",
      "insecure": "true",
      "username": "{{user `vcenter_username`}}",
      "password": "{{user `vcenter_password`}}"
    }
  ]
}