PSDSC_Config.ps1

configuration MyConfig {
    Param()
    if($Node.Role -contains 'DHCPData' -and $Node.Customers -eq 'CustomerA') {
        $Domain = $ConfigurationData.customerA.Domain
    }
    else {
        $Domain = $ConfigurationData.DefaultDomain.Domain
    }
    File MyDomainFile {
        Ensure = 'Present'
        DestinationPath = "C:\Domain.txt"
        Contents = "$Domain"
    }
}