The default profile with a flag next to it in the speech control panel is determined by the registry entry:
[HKEY_CURRENT_USER\Software\Microsoft\Speech\RecoProfiles]
"DefaultTokenId"="HKEY_CURRENT_USER\\SOFTWARE\\Microsoft\\Speech\\RecoProfiles\\Tokens\\{A32BEAC3-4442-4E13-B485-8A2DD7178794}"
, GUI/ Windows Speech Recognition. " ".
SetRecoProfile. , , , ...