Access Telemetry Client to add customDimensions for App Insights

Question. Is it possible to access and add customDimensions / properties to the existing telemetry client within the function app? Specifically for a request. I'm able to do so only when creating a new client and invoking trackRequest, like so:

```
class MyInitializer3 : Extensibility.ITelemetryInitializer {
<# Define the class. Try constructors, properties, or methods. #>
[void]Initialize([Channel.ITelemetry]$Telemetry){
#$requestTelemetry = [DataContracts.RequestTelemetry]::new()
$requestTelemetry = [DataContracts.RequestTelemetry]$Telemetry

$requestTelemetry.Properties["test"] = "test value"
}
}

$requestTelemetry = [DataContracts.RequestTelemetry]::new()

######################

$telemetryConfig = [Microsoft.ApplicationInsights.Extensibility.TelemetryConfiguration]::CreateDefault()
$telemetryConfig.ConnectionString = "XXXXXXXX"

$telemetryConfig.TelemetryInitializers.Add( [MyInitializer3]::new() )

$client = [Microsoft.ApplicationInsights.TelemetryClient]::new($telemetryConfig)

$client.TrackRequest("requestTest",$(get-date),100,201,$true)
```

But of course the function app already logs a request anyway, and I'd like to add to that.