The file that these setting use is ${baseidr}/fusionpbx/app/scripts/resources/scripts/app/voicemail/resources/functions/record_message.lua
None of the options there (presumably custom) fit, or I don't believe they will work, for mod_unimrcp.
I have looked at this one as well but I did find that on further review I don't have the file mentioned at the very end on my system - applications/voicemail_transcription.rst . That would seem to be important. Maybe that is my missing link. Have you been able to get mod_unimrcp working for vm transcription? I would think it is a fairly common thing to do with unimrcp and freeswitch.
Thanks for your help,