[IvanDSaboya]

this should work . I modified the pitch and speed using this codes before the text I wanted to modify. 
howeverIi didnt achieve to work in the $username$ field, but just in the $message$.

try this example as a message first:

 <volume level="100"> hey how is everything <volume level="50"> hey how is everything 

see more here: (not everything works, but play with it.)

XML TTS Tutorial (SAPI 5.3) | Microsoft Learn