Voicemod can modify incoming voice through another application, e.g.: Caster Live.
This is how to set up Voicemod with Caster Live to modify an audio file:
Caster Live settings:
You have to add VLC (or any other sound player), enabling Stream and disabling Monitor and the Voicemod microphone (not the Voicemod application), disabling Stream and enabling Monitor. Then play the audio file through VLC (or the player you have added), and send the audio to Voicemod via CASTER Stream Mix 1 as Microphone in Voicemod.
If you want to monitor the audio modification, you have to enable Hear Myself in Voicemod.
Finally, click on the record button to have the file with the modified audio (Monitor Mix).
MORE INFO about Caster Live: https://gingeraudio.com/docs/groundcontrol-caster-manual/