Once a MIDI track has been recorded in your audio program, select a virtual instrument to playback the MIDI data. The MIDI information will remain the same but you can still change the playback sound while in MIDI form. Make any edits to MIDI notes and velocities and tweak the settings on your virtual instrument to ensure you are satisfied. Once the MIDI is exported as a sound file making changes can only be executed through normal audio processes.
To ensure that only the selected MIDI track is going to be exported as a sound file, solo the track so that no other files are heard during playback.
In your digital audio workstation, you will have the ability to "bounce," "render" or "export" your session to any number of file formats available. These words generally mean the same thing, yet are called different things in different programs. Select the best option for your software and choose ".wav" as the file format. Save the file to your session's audio files folder and name it accordingly. You now have an audio file created from the MIDI track which you can send or import back into your session.