sample gist to append to the configurecloudservice.ps1 (or you can add a new ps1) to access custom settings defined for the Cloud Service

append_configurecloudservice.ps1

TRY {
    # search for the Dll
    Write-Verbose -Message "Creating credential object"
    $Splathashtable = @{
                        'Path' = "$env:windir\Microsoft.NET\assembly\";
                        'Filter' = 'Microsoft.WindowsAzure.ServiceRuntime.dll';
                        'Include' = '*.dll'
                        }
    $dllfile = Get-ChildItem @Splathashtable -Recurse  | Select-Object -Last 1 # selecting only one object, in case of multiple results
    Write-Verbose -Message "ServiceRuntime dll found"
    
    # add the DLL to the current PowerShell session
    Add-Type -Path $dllfile.FullName    
    Write-Verbose -Message "ServiceRuntime dll added to the current runspace"

    # Call the Static method on the class to retrieve the setting value
    $Setting = [Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment]::GetConfigurationSettingValue('TestKey')
    Write-Verbose -Message "Fetched Username TestKey from the Service Configuration"

    # Now use the value as you please
    Write-Verbose -Message "Value stored in TestKey is $Setting"
}
CATCH {
    throw $_.exception

}