The result of the Apply-VMHostProfile is a hash table, so you'll have to use the Get-Enumerator function to retrieve the key and the value.
Something like this
$hprof=Get-VMHostProfile-Name"My HostProfile"
$AdditionalConfiguration=Apply-VMHostProfile-Profile$hprof-EntityMMMSTV004*-ApplyOnly-Confirm:$false
$AdditionalConfiguration.GetEnumerator() |
SelectKey|
Export-Csvc:\hprof.csv-NoTypeInformation-UseCulture
Thanks for drawing our attention to that mistake.