You can add tremolo to an audio file. Google/Bing adding vibrato or tremolo to an audio file and you will find some programs/VSTs that can do just that. The free Audacity with all of the added effects can do it also. When using Audacity you would have to bring in your RT, add your effect(s), then bring it back into either BiaB (if possible - don't know never tried it) or into a DAW.

Adding vibrato or Tremolo to a MIDI file depends on your sound source. I have Vibes and other sounds, including the SWAM instruments, that can add the effect via a CC number, usually CC1, the mod wheel.

I hope this helps and good luck.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware