This script inserts guestinfo to a VM configuration parameters. "guestinfo" settings can be read from Guest OS in order to customize network settings for example.

GuestInfoCustomization.ps1

# load PowerCli Snapin
if ((Get-PSSnapin -Name VMware.Vimautomation.Core -ErrorAction SilentlyContinue) -eq $null ) {
    Add-PsSnapin VMware.Vimautomation.Core
}

# vCenter server
$VC = "vcenter.domain"
$Username = "domain\user"

# connecting vCenter
$Credentials = get-credential  -credential $Username
Connect-VIServer -server $VC -Credential $Credentials

# create a list of infos for the guest OS
$customization = @{
	"hostname"  = "happy-debian";
	"ipaddress" = "192.168.109.18";
	"netmask"   = "255.255.255.0";
	"gateway"   = "192.168.109.1";
	"dns1"      = "192.168.109.2";
	"dns2"      = "192.168.109.3";
}

# create a reconfiguration task object
$vmConfigSpec = New-Object VMware.Vim.VirtualMachineConfigSpec

# add each information to the previous object
foreach ($info in $customization.GetEnumerator()) {
    Write-Host "setting $($info.Name): $($info.Value)"
	$extra = New-Object VMware.Vim.optionvalue
	$extra.Key="guestinfo.$($info.Name)"
	$extra.Value=$info.Value
	$vmConfigSpec.extraconfig += $extra
}

# select the virtual machine and apply changes
$vm = Get-View -ViewType VirtualMachine | where { $_.name -eq "deb7GuestInfo" }
$vm.ReconfigVM($vmConfigSpec)

# clean leave
Disconnect-VIServer -Confirm:$false